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Proceedings, The 15th Congress of FAVA
FAVA -OIE Joint Symposium on Emerging Diseases
27-30 October
Bangkok, Thailand
Bacterial Foodborne Diseases
John N. Sofos
University Distinguished Professor Colorado State University
Director, Center for Meat Safety & Quality
Leader, Food Safety Cluster of Infectious Diseases Supercluster
Department of Animal Sciences; 1171 Campus Delivery Fort Collins, Colorado 80523-1171, USA
Telephone: (970) 491-7703; Facsimile: (970) 491-5326 Mobile (Cell): (970) 217-2239
E-mail: [email protected] http://ansci.colostate.edu
Keywords : Foodborne Diseases, Bacterial
chronic sequelae, including (Bacon and Sofos,
2003) : campylobacteriosis : arthritis, carditis,
cholecystitis, colitis, erythema nodosum, GuillainBarre syndrome, hemolytic-uremic syndrome,
meningitis, pancreatitis, septicemia; listeriosis:
meningitis, meningoencephalitis,abortion, stillbirths,
septicemia, etc; salmonellosis: aortitis, cholecystitis,
colitis, epididymoorchitis, meningitis, endocarditis,
myocarditis, osteomyelitis, pancreatitis, Reiter’s
disease,septicemia,thyroiditis,rheumatoid syndrome,
septic arthritis, splenic abscesses; shigellosis:
hemolytic uremic syndrome, erythema nodosum,
peripheral neuropathy, pneumonia, Reiter’s disease,
septicemia, synovitis, splenic abscesses; yersiniosis:
arthritis, erythema nodosum, septicemia, spondylitis,
Still’s disease, pyomyositis, cholangitis, splenic and
liver abscesses; enterohemorrhagic Escherichia coli
(EHEC) : hemolytic uremic syndrome, erythema
nodosum, seronegative arthropathy
(http://www.foodsafety.gov/~mow/intro.html).
Biological pathogens were documented as agents of
foodborne illness in the following periods. 18301960: Trichinella spiralis, Taenia solium, Taenia
saginata, Salmonella, Staphylococcus aureus, Vibrio
cholerae, Clostridium botulinum nonproteolytic B,
Streptococcus pyogenes (Group A), Clostridium
botulinum types A and proteolytic B, Shigella,
Streptococcus group D, Clostridium botulinum type
E, Clostridium perfringens, Vibrio parahaemolyticus, Hepatitis A virus, Bacillus cereus (diarrheal
type). 1961-1970: Enteropathogenic Escherichia
coli, Plesiomonas. 1971-1980: Bacillus cereus
(emetic type), Campylobacter, Enteroinvasive
E. coli, Noroviruses, Yersinia enterocolitica. 19811990 : Aeromonas, Enterohemorrhagic E.coli
O157:H7 and other Shiga toxin-producing E. coli
(STEC), Cryptosporidium, Listeria monocytogenes,
Vibrio vulnificus. 1991-2000: Cyclospora, resistant
bacteria, and prions. Bacteria commonly causing
foodborne diseases in recent years include species or
serotypes of the Gram-negative genera Campylobacter, Salmonella, Escherichia, Shigella, Yersinia
and Vibrio, while Gram-positive pathogenic genera
include Listeria, Staphylococcus, Bacillus and
Clostridium. In addition, there are certain other
pathogenic bacteria with the potential of being
foodborne. A brief description of common
foodborne bacterial pathogens follows.
Introduction
Despite the extensive scientific progress and major
technological developments achieved in recent
years, millions of foodborne bacterial disease
episodes occur every year in the United States and
cause thousands of deaths, with annual economic
losses of approximately 8.4 billion dollars (Mead et
al., 1999). Specifically, according to estimates by
the United States Centers for Disease Control and
Prevention (CDC), foodborne diseases cause
approximately 76 million illnesses, 325,000
hospitalizations, and 5,000 deaths in the United
States each year, a large proportion of which are of
unknown etiology. According to the estimates,
pathogenic bacteria cause approximately 30% of all
foodborne illnesses of known etiology, and
approximately 1,300 deaths annually, or 72% of
total deaths attributed to contaminated foods (Mead
et al., 1999). It is important to recognize, however,
that most foodborne disease episodes remain
unreported or undiagnosed. Specifically, unknown
agents are responsible for an estimated 62 million
illnesses and 3,200 deaths annually in the United
States, while an estimated 14 million illnesses and
1,800 deaths are of known etiology (Mead et al.,
1999; Bacon and Sofos, 2003).
Foodborne and waterborne pathogenic bacteria are
known as agents of disease for almost 200 years,
well before food microbiology became an
established scientific field (Bacon and Sofos, 2003).
Presently, bacterial foodborne diseases are classified
as infections, intoxications and toxicoinfections. An
infection involves invasion of the host by cells of the
microorganism, which, after being established in the
host, proliferate and cause illness. Intoxication or
poisoning is the result of consuming a food in which
a microorganism has grown and produced a toxin,
which causes the disease. A toxicoinfection involves
invasion of the host by the pathogen and production
of toxin in the host. Thus, a food may be the vehicle
of transmission for the hazard (infection) and/or of
metabolic toxic products (intoxication).
Common clinical symptoms of most foodborne
diseases are diarrhea, vomiting, fever, nausea, and
other manifestations in the gastrointestinal tract.
Certain pathogens cause syndromes associated with
the central nervous system or various organs, while
some may result in various complications and
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Proceedings, The 15th Congress of FAVA
FAVA -OIE Joint Symposium on Emerging Diseases
27-30 October
Bangkok, Thailand
Lund et al., 2000; Bacon and Sofos, 2003; Doyle
and Beuchat, 2007).
Common Foodborne Pathogenic Bacteria
Bacillus cereus
This foodborne pathogenic bacterium was first
isolated and described in 1887, while in the early
1950s it was recognized as an agent of foodborne
disease. Bacillus cereus is a member of the family
Bacillaceae, which are spore-forming, Grampositive, motile rods. The vegetative cells grow
anaerobically, while they sporulate freely in the
presence of oxygen. As other Bacillus species it is
found in soil and water environments.
Its
endospores can survive and may be found in the
environment and in dried foods such as spices and
cereal products. B. cereus is estimated to cause
approximately 27,000 cases of foodborne illness and
a small number of deaths annually in the United
States (Doyle, 1989; Mead et al., 1999; Murray et
al., 1999; Lund et al., 2000).
Depending on strain, vegetative cells of B. cereus
grow at 4-15 to 35-55°C, preferring the range 3040°C. The pH range allowing growth is 4.9-9.3;
however, in foods such as meat it may grow at pH
values as low as 4.35. The minimum water activity
(aw) allowing growth is 0.93, with 0.912 being
recommended as the minimum for controlling
growth in fried rice. Spores generally germinate at
5-50°C, with an optimum at 30°C, while under
laboratory conditions the spores germinate in the
range –1 to 59°C (ICMSF, 1996; Bacon and Sofos,
2003).
B. cereus causes emetic or diarrheal illness;
syndromes are caused by distinct toxins formed
when endospores survive the cooking process,
germinate, and proliferate during storage. Foods
associated with the diarrheal illness include
contaminated meats, vegetables, pastas and soups.
Symptoms include abdominal pain, nausea and
diarrhea after an incubation period of 8-16 h, and
persist for no longer than 12-24 h. The emetic
syndrome is associated with consumption of foods
containing rice, as well as cream, potatoes and
vegetable sprouts. The incubation period of the
emetic syndrome is 1-5 h, and common symptoms
include vomiting and nausea, and they persist for 624 h. The emetic toxin may be associated with liver
failure. The diarrheal illness is caused by a heat
labile enterotoxic complex, while the emetic type is
associated with a thermostable toxin. The diarrheal
enterotoxin protein shows optimum activity at 3237°C and it is inactivated at 56°C for 5 min. It is
sensitive to proteases (e.g., trypsin and pepsin) and
unstable at pH values outside the range 4.0-11.0.
The emetic toxin has optimum activity at 25-30°C,
maintains activity at 126°C for 90 min, is stable at
pH valus of 2.0-11.0, and is resistant to trypsin and
pepsin. The infectious dose of B. cereus is estimated
to be in the range of 200 to 109 cells per g,
depending on strain. In general, food containing 104
cells per g should not be considered safe for human
consumption (Doyle, 1989; Murray et al., 1999;
Campylobacter
The organism (previously Vibrio fetus) was first
isolated in 1909, but only since the late 1970s it
became known as a cause of foodborne
gastroenteritis, known as campylobacteriosis or
Campylobacter enteritis. In the past 10-15 years
Campylobacter jejuni is recognized as the first or
second (after Salmonella) most common cause of
bacterial foodborne illness in the United States; it is
estimated to be associated with 2.0-2.5 million cases
annually and has a case fatality rate of 0.001 (Mead
et al., 1999; Bacon and Sofos, 2003).
Campylobacter and Arcobacter (which until recently
was included in Campylobacter) are members of the
family Campylobacteraceae which includes 18 and
four species and subspecies within each genus,
respectively. Campylobacter is associated with
poultry and migratory birds, while other sources
include rodents, natural water sources, and insects.
The most common foodborne species are C. jejuni
and C. coli (Murray et al., 1999; Bacon and Sofos,
2003).
The cells are curved, slender, Gram-negative
nonspore-forming rods, and are characterized by a
corkscrew-type motility. As microaerophilic, they
grow optimally at 2.0-5.0% oxygen and 5.0-10.0%
carbon dioxide, while growth is inhibited by 21%
oxygen. The optimum temperature range for growth
of Campylobacter is 37-42°C, while under favorable
nutritional,
atmospheric
and
environmental
conditions, growth occurs between 30 and 45°C.
They grow at pH values 4.9-8.0, but prefer pH 6.57.5. As they are sensitive to drying, Campylobacter
require an aw above 0.912 (ICMSF, 1996; Lund et
al., 2000).
Campylobacteriosis may result from ingestion of as
few as 500 cells. Symptoms appear within 2-5 days,
may persist for up to 10 days, and include acute
colitis, fever, malaise, abdominal pain, headache,
watery or sticky diarrhea with traces of blood
(occult), inflammation of the lamina propria, and
abscesses (Lund et al., 2000; Bacon and Sofos,
2003).
Foods commonly implicated in Campylobacter
infections include milk, eggs, meats, poultry, and
water. The pathogenesis of the infection is not well
understood; however, it is believed that C. jejuni or
C. coli result in extraintestinal interaction with
cellular constituents as indicated by high serum IgG
and IgM antibody levels following infection.
Determinants of Campylobacter virulence include
motility, adherence, invasion, and toxin production.
Toxins produced include a heat-labile enterotoxin
(i.e., denatured at 56°C for 1 h) which is destroyed at
pH 2.0 or 8.0, a trypsin-sensitive cytotoxin, which is
more heat-stable than the enterotoxin (i.e., denatured
at 60°C for 30 min), and a cytolethal distending
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Proceedings, The 15th Congress of FAVA
FAVA -OIE Joint Symposium on Emerging Diseases
27-30 October
Bangkok, Thailand
adequate to inactivate spores of Group I strains.
Foodborne botulism has been traditionally
associated with under-processed and abused
sausages or home-canned foods; however, in recent
years botulism has been acquired through
consumption of contaminated foods such as potato
salad, sautéed onions, garlic sauce, cheese, yogurt,
bean paste, bamboo shoots, and olives (Lund et al.,
2000; Bacon and Sofos, 2003).
Symptoms of botulism appear 12-36 h after
consumption of food containing the toxin. Initially,
symptoms may include nausea and vomiting, but
these symptoms are followed by more characteristic
neurological signs of visual impairment and acute
flaccid paralysis which through the muscles of the
face moves to the pharynx, the thorax and
extremities, and leads to death due to respiratory
failure caused by paralysis of the upper airway or
diaphragm. The neurotoxins are synthesized during
cellular growth, are released during cell lysis, and
become activated through proteolytic cleavage
(Murray et al., 1999; Lund et al., 2000; Bacon and
Sofos, 2003).
toxin (CDT) (Doyle, 1989; Murray et al., 1999;
Bacon and Sofos, 2003).
Clostridium botulinum
The pathogen causes classical foodborne botulism
through ingestion of preformed toxin in foods,
wound botulism resulting from toxin production in
an infected wound, infant botulism due to toxin
production in the intestinal tracts of infants, and
botulism through intestinal colonization of
individuals with lack of microbial competition. The
pathogen was identified after its isolation from a
ham-type product that was involved in illness in
1897; however, botulism-type illnesses had been
associated with consumption of sausages earlier in
the 1800s. Infant botulism is the most common
form of the disease in the United States after it was
first recognized in 1976. In recent years, foodborne
botulism cases in the United States are less than 100
per year, with a case fatality rate of 0.0769 (Mead et
al., 1999; Lund et al., 2000; Doyle and Beuchat,
2007).
Clostridium is an anaerobic or aerotolerant Grampositive, sporeformer of the family Bacillaceae. The
vegetative cells appear as straight or curved rods,
varying from short coccoid rods to long filamentous
forms with rounded, tapered or blunt ends that occur
singly, in pairs or in various chain lengths. Spores
are found widely in the environment, and especially
in soil, water and in the intestinal tract of animals
(Bacon and Sofos, 2003).
Cells of C. botulinum are motile and produce
neurotoxins, the most lethal poison known. The
seven known types of botulinum neurotoxins are A
through G, with types A, B, E and F causing
botulism in humans, types C and D causing botulism
in birds and mammals, and type G which has not
been associated with a botulism case. Group I
includes type A strains which are proteolytic and the
proteolytic strains of types B and F, while Group II
includes all type E strains and the nonproteolytic
type B and F strains; Group III includes type C and
D strains, and Group IV includes type G strains.
Groups I and II are most commonly implicated in
human botulism cases (Murray et al., 1999; Lund et
al., 2000; Bacon and Sofos, 2003).
Group I strains grow at 10-48°C, with an optimum at
37°C, and their spores are very heat resistant (D100°C
value of 25 min). These strains grow above pH 4.6,
in sodium chloride concentrations below 10%, and
require a minimum aw of 0.94. Group II
nonproteolytic strains grow at temperatures as low
as 3.3°C with an optimum at 30°C; spores of Group
II strains are not as resistant to high temperatures
(D100°C value of less than 0.1 min). The minimum
pH of Group II strains is 5.0, the maximum sodium
chloride concentration less than 5%, and the
minimum aw is 0.97. The neurotoxins are resistant
to freezing but sensitive to heat (75-80°C). Low
acid, moist foods are made shelf-stable and safe
from botulism by thermal processing (canning)
Clostridium perfringens
The species was first recognized as an agent of
foodborne disease in the 1940s, even though it was
known to be associated with gastroenteritis since
1895. United States estimates indicate that it causes
approximately 250,000 cases of foodborne illness
annually with a case fatality rate of 0.0005 (Mead et
al., 1999; Bacon and Sofos, 2003).
The spore-forming organism (previously known as
Clostridium welchii) is a member of the family
Bacillaceae. The cells are nonmotile, rod-shaped,
and produce proteinaceous toxins. The vegetative
cells grow at 6-50°C, with optimum growth at 4347°C, a minimum aw of 0.93, a sodium chloride
concentration of less than 5-8% depending on strain,
and pH values of 5.0-9.0, while the range 6.0-7.2 is
preferred (Doyle, 1989; ICMSF, 1996; Bacon and
Sofos, 2003).
The spores and cells of C. perfringens are present in
the soil and can contaminate foods such as meat and
shellfish. It causes wound infections as well as
syndromes such as myonecrosis, clostridial cellulitis,
intra-abdominal sepsis, gangrenous cholecystitis,
postabortion infection, intravascular hemolysis,
bacteremia, pneumonia, thoracic and subdural
empyema, and brain abscesses (Murray et al., 1999;
Lund et al., 2000).
The pathogen also causes a rare foodborne necrotic
enteritis, known as Darmbrand or Pig-Bel, as well as
type A food poisoning, which requires ingestion of a
highly contaminated food (>106 cells). High
contamination is necessary because many of the
cells are killed by the acid of the stomach.
Temperature abuse, improper slow cooking and slow
cooling of meat or meat products, or insufficient
reheating, allow surviving spores to germinate and
vegetative cells to proliferate, leading to foodborne
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Proceedings, The 15th Congress of FAVA
FAVA -OIE Joint Symposium on Emerging Diseases
27-30 October
Bangkok, Thailand
0.95. Although their optimum pH is 6.0-7.0, they
can grow in the range 4.4-9.0, and they are known to
tolerate acid more than other pathogens (Bacon and
Sofos, 2003; Samelis and Sofos, 2003; Doyle and
Beuchat, 2007).
Non-pathogenic as well as diarrheagenic E. coli
strains are commonly found in the gastrointestinal
tracts of mammals and become fairly ubiquitous in
the environment. Human illness results through
fecal-oral transmission, and through contaminated
water or foods of animal or plant origin. In the past,
the majority of outbreaks have been associated with
consumption of undercooked ground beef. Other
foods that have served as vehicles for transmission
include water, cantaloupes, apple juice/cider,
potatoes, coleslaw, radish and alfalfa sprouts,
lettuce, and spinach (Bacon and Sofos, 2003).
Common STEC serotypes such as O157:H7,
O157:NM, O11:H8, O111:NM, and O26:H11 can
cause mild diarrhea, severe bloody diarrhea
(hemorrhagic colitis) or in some cases hemolytic
uremic syndrome (HUS), characterized by
microangiopathic hemolytic anemia, thrombocytopenia and acute renal failure. The symptoms appear
3-9 days after ingestion of >10 cells and last for 2-9
days. It is estimated that serotype O157 is involved
in 80% of the HUS cases in North America, while
approximately 6% of individuals infected with
STEC serotype O157 develop HUS. In addition to
O157:H7, which is the most prevalent diarrheagenic
STEC in the United States, other serotypes are also
associated with HUS and related syndromes (Blaser
et al., 1995; Bacon and Sofos, 2003).
The ETEC infection has an incubation period of 1450 h and its symptoms are watery diarrhea,
abdominal cramps, low-grade fever, nausea and
headache. Symptoms may last for 3-19 days. The
infective dose exceeds 107 cells, and it is a common
cause of traveler’s diarrhea. The case fatality rate in
developed countries is 0.0001 (ICMSF, 1996; Mead
et al., 1999).
EPEC is a common cause of infantile diarrhea with a
presumably low infective dose in infants and young
children and a high infective dose in adults (>106
cells). Symptoms appear after 29-72 h and include
severe, prolonged diarrhea, vomiting and fever in
children. Occasionally, the stools may contain
blood, and symptoms may persist for 6 h to 3 days.
Shedding of cells may continue for up to 2 weeks
(Murray et al., 1999; Bacon and Sofos, 2003).
EIEC is a form of bacillary dysentery and has an
incubation period of 8-24 h. During the incubation
period, the infected individual may be asymptomatic
or may experience watery diarrhea followed by
bloody stools. Most infected individuals suffer only
watery diarrhea for a few days or weeks. The
infectious dose appears to be >106 cells, and the
mild dysentery is similar to that caused by Shigella
(Bacon and Sofos, 2003).
The pathogenetic process differs among various
serotypes following intestinal colonization. STEC
illness. The incubation period is 7-30 h, and typical
symptoms include abdominal pain, diarrhea, nausea
and vomiting, and persist for 24-48 h (Murray et al.,
1999; Bacon and Sofos, 2003; Doyle and Beuchat,
2007).
Toxin types of C. perfringens include A through E,
while all strains produce an alpha-toxin
(phospholipase) involved in myonecrosis. Almost
all reported foodborne gastroenteritis cases in the
United States are a result of type A infection. Cells
surviving through the stomach, sporulate and
produce enterotoxin in the small intestine, which is
released during cell lysis. The enterotoxin then
binds to epithelial cells, and causes cytotoxic cell
membrane damage and subsequent alteration of
permeability leading to diarrhea and abdominal
cramps (Lund et al., 2000; Bacon and Sofos, 2003;
Doyle and Beuchat, 2007).
Diarrheagenic Escherichia coli
The organism was first known as Bacterium coli and
was isolated by Dr. Theodor Escherich in the late
1800s. By the 1940s, it was associated with
gastroenteritis and mortality in infants. Shiga toxinproducing E. coli (STEC) was associated with
foodborne illness in 1982. Currently, diarrheagenic
E. coli is estimated to be implicated in over 170,000
cases of foodborne disease annually in the United
States, with a case fatality rate of 0.0083 for STEC
serotypes (ICMSF, 1996; Mead et al., 1999; Bacon
and Sofos, 2003).
Diarrheagenic or enterovirulent E. coli serotypes are
members of the E. coli species and belong to the
family Enterobacteriaceae. They are Gramnegative, facultatively anaerobic, nonspore-forming,
mostly motile rods. Diarrheagenic E. coli can be
categorized into: (1) Shiga-toxin or verocytotoxinproducing E. coli (STEC or VTEC), which include
the enterohemorrhagic E. coli (EHEC) strains
(approximately 112 serotypes); the most common
serotypes
isolated
from
individuals
with
diarrheagenic E. coli are O157 : H7 and O157 :
nonmotile. (2) Enterotoxigenic E. coli (ETEC),
which include approximately 32 serotypes and
produce a heat-labile (LT) enterotoxin, and/or a
heat-stable (ST) enterotoxin. (3) Enteropathogenic
E. coli (EPEC) with approximately 23 noninvasive
and no toxin producing serotypes. (4) Enteroinvasive
E. coli (EIEC) of approximately 14 nonmotile
serotypes, which have the ability to invade
peripheral host tissues. Additional diarrheagenic
E. coli categories or groups, include enteroaggre gative E. coli (EAEC), diffusely adherent E. coli
(DAEC), necrotoxic or cell-detaching E. coli (NTEC
or CDEC) and cytolethal distending toxin (CLDT or
CDT)-producing E. coli, with no established clinical
or foodborne significance (Murray et al., 1999;
Bacon and Sofos, 2003).
The pathogen can grow at temperatures as low as
7-8°C and as high as 44-46°C, with an optimum in
the range 35-40°C, and a minimum required aw of
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Proceedings, The 15th Congress of FAVA
FAVA -OIE Joint Symposium on Emerging Diseases
27-30 October
Bangkok, Thailand
fatality rate in excess of 0.2 (Mead et al. 1999;
Bacon and Sofos, 2003).
The genus Listeria includes the species
L. monocytogenes, L. innocua, L. ivanovii,
L. seeligeri, L. welshimeri, and L. grayi, which now
includes L. murrayi. L. monocytogenes are
Nonsporeforming, psychrotrophic, aerobic,
microaerophilic or facultatively anaerobic, Grampositive rods that are motile at 28°C (Ryser and
Marth, 2007).
The organism is hardy and widely spread throughout
the environment. It is a major concern to the food
industry because it grows under conditions of high
humidity, low temperatures, and limited nutrient
levels, such as in floor drains, stagnant water, floors
and food residues on processing equipment (Ryser
and Marth, 2007).
Of the 13 known L. monocytogenes serovars, 1/2a,
1/2b and 4b, account for 95% of human isolates,
with serovar 4b strains involved in 33-50% of
human cases worldwide.
Strains show major
differences in virulence; however, no major
correlation has been established between virulence
and origin (human, animal, food, etc.) or
characteristics (serovar, genotype, etc.). At this time,
all strains of L. monocytogenes are considered
capable of causing listeriosis (Lund et al., 2000;
Bacon and Sofos, 2003; Doyle and Beuchat, 2007).
The pathogen grows at temperatures as low as –
0.4°C and as high as 45°C, with optimum growth at
30-37°C. The pH range allowing growth is 4.399.40, with optimum growth at pH 7.0. Growth
requires an aw above 0.92, while the pathogen
survives at sodium chloride levels of up to 30%
(ICMSF, 1996; Bacon and Sofos, 2003).
Instead of being a typical gastrointestinal foodborne
illness, listeriosis is characterized by a variety of
serious syndromes of the central nervous system
such as meningitis and meningoencephalitis.
Pregnant women may experience a flu-like illness,
while the fetus is affected by meningitis, neonatal
septicemia, stillbirth, fetal death or spontaneous
abortion (Murray et al., 1999; Bacon and Sofos,
2003; Doyle and Beuchat, 2007).
The incubation period of listeriosis may be as long
as a few days to 2-3 months. The pathogen affects
mostly immunocompromised individuals exhibiting
a case-fatality rate of 20-30% and 38-40% among
immunocompromised individuals.
Additional
complications of listeriosis have been reported in as
many as 30% of individuals surviving a central
nervous system infection. The infectious dose
should be greater than 100 cells/g; however, the
possibility of lower infectious doses should not be
ignored, especiall for sensitive individuals (Bacon
and Sofos, 2003; Doyle and Beuchat, 2007; Ryser
and Marth, 2007).
When contaminated food is consumed, cells of the
pathogen, if present, may cross the intestinal barrier,
become internalized by macrophages and then
transported to lymph nodes via the blood stream;
produce either Shiga toxin 1 (Stx1), which is
essentially identical to the Shigella dysenteriae type
1 toxin, Shiga toxin 2 (Stx2), or a combination of
both
toxins.
The
Shiga-like
toxins,
or
verocytotoxins, are the major virulence factor,
resulting in death in certain individuals. In addition
to Shiga toxins, virulence factors include a plasmid
encoded enterohemolysin; a heat stable enterotoxin;
plasmid encoded catalase-peroxidase and serine
protease enzymes, an outer membrane protein
synthesized in response to a low iron environment,
an intestinal adherence factor (e.g., intimin), and the
presence of O157 antigen which may enhance the
cytotoxicity of Shiga toxins (Bacon and Sofos,
2003).
ETEC produce heat-labile (LT) and/or heat-stable
(ST) enterotoxins. However, most of the outbreaks
in the United States have been associated with
strains producing ST only or together with LT.
After colonization, ETEC secrete the enterotoxins,
which enter into intestinal epithelial cells via
endocytosis, and result in elevated intracellular
cyclic AMP and GMP levels, and intestinal lumen
fluid accumulation (Murray et al., 1999; Bacon and
Sofos, 2003).
Colonization by EPEC causes effacement of
microvilli resulting in adherence to the epithelial cell
membrane. Presence of the EPEC adherence factor
plasmid determines the ability to adhere, by an outer
membrane protein called intimin that is encoded by
the eae gene. Signal transduction causes the release
of intracellular calcium, inducing a calciumdependent actin severing protein which causes
cytoskeletal rearrangements that may include the
concentration of polymerized actin resulting in the
formation of a “pedestal”. In addition to pedestal
formation, increased intracellular calcium inhibits
uptake and stimulates fluid efflux into the intestinal
lumen (Bacon and Sofos, 2003).
Pathogenesis by EIEC involves penetration of the
epithelium of the colonic mucosa, and entrance into
the cell through endocytosis. This occurs through
production of several outer membrane polypeptides.
Lysis of the surrounding endocytic vacuole is
followed by production of one or more secretory
enterotoxins, as intracellular replication proceeds.
Then, EIEC migrate through the cytoplasm and
extend into adjacent epithelial cells (Bacon and
Sofos, 2003).
Listeria monocytogenes
The pathogen was first described in the 1910s and
the first reported human case involved a soldier
inflicted with meningitis during World War I;
however, foodborne transmission was not
documented until 1981.
Because of its high
mortality rate, listeriosis, is considered a major
foodborne infection. Available estimates indicate
that L. monocytogenes is responsible for
approximately 2,500 cases of foodborne disease in
the United States annually with an estimated case
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Proceedings, The 15th Congress of FAVA
FAVA -OIE Joint Symposium on Emerging Diseases
27-30 October
Bangkok, Thailand
activates adenyl cyclase causing increased cyclic
AMP concentrations in the cytoplasm. In addition to
the enterotoxin, a thermolabile cytotoxin is also
formed and released extracellularly in response to
environmental stress. The cytotoxin inhibits protein
synthesis and promotes cell lysis, facilitating cell
dissemination in the host tissue (Lund et al., 2000;
Bacon and Sofos, 2003).
eventually they are transported to the liver, which is
the primary site of infection. Internalized cells cause
lysis of vacuoles and are released into the cytosol
where they multiply. Through polymerization and
redistribution of actin the cells can spread directly
from one cell to another, thus spreading through
tissue without leaving the intracellular environment
and subsequently remaining protected from host
antibodies (Bacon and Sofos, 2003).
Shigella
Bacillary dysentery is known since 1898 and is
caused by Shigella which was first described by
Shiga during an epidemic in Japan. Shigella is
estimated to be involved in about 90,000 cases of
foodborne disease annually in the United States,
with a case fatality rate of 0.0016 (ICMSF, 1996;
Mead et al., 1999; Murray et al., 1999).
It is a member of the family Enterobacteriaceae and
its four serogroups have been traditionally treated as
species: serogroup A as S. dysenteriae, serogroup B
as S. flexneri, serogroup C as S. boydii, and
serogroup D as S. sonnei. Serogroups A, B and C
consist of 38 serotypes, while serogroup D contains
only one. The organism is nonspore-forming,
facultatively anaerobic Gram-negative rods. It
grows at 6-48°C, with an optimum at 37°C. Growth
is optimal at pH 6.0-8.0, with minimum and
maximum limits at 4.8 and 9.3, respectively
(ICMSF, 1996; Doyle and Beuchat, 2007).
The organism is found in environments of poor
sanitation and hygiene. The primary route of
transmission is through person-to-person contact,
while foods associated with outbreaks of shigellosis
include milk, salads, chicken, shellfish, onions, and
other fresh produce.
In the United States,
approximately 20% of all cases are associated with
international travel (ICMSF, 1996; Bacon and Sofos,
2003; Doyle and Beuchat, 2007).
The infectious dose of Shigella is as low as 5,000
cells, but some individuals may develop symptoms
after ingestion of as few as 10-200 cells. The
incubation period is 12-50 h, and common
symptoms include watery diarrhea, fever, fatigue,
malaise and abdominal cramps, while classic
dysentery is characterized by scant stools containing
blood, mucus and pus may follow. Even though
severe, shigellosis is self-limiting, generally lasting
1-2 weeks or up to a month. S. dysenteriae type 1 is
the most frequent cause of epidemic dysentery or the
most severe form of the illness which may also
include HUS; dysentery may be caused by all four
Shigella serogroups. S. flexneri infection has also
been associated with Reiter’s chronic arthritis
syndrome (Blaser et al., 1995; Lund et al., 2000;
Doyle and Beuchat, 2007).
Classic dysentery is the result of extensive
colonization and invasion of the colonic mucosa and
induction of phagocytosis and subsequently
triggering of an acute inflammatory response. In
addition to the Shiga toxins produced by S.
dysenteriae type 1, S. flexneri type 2a has been
Salmonella
Salmonella Typhi was discovered in 1880 as the
etiologic agent of typhoid fever. In 1900 the
organism was named after Dr. Salmon who worked
on S. Cholerae-suis isolated from swine suffering
from hog cholera. Salmonella is currently the first
or second most common bacterium implicated in
foodborne disease outbreaks in the United States,
with a case fatality rate of 0.0078 (ICMSF, 1996;
Mead et al., 1999).
Salmonella is a member of the Enterobacteriaceae
family, which are Gram-negative, facultatively
anaerobic, nonspore-forming rods. The genus has
two recognized species, S. enterica with six
subspecies, and S. bongori. Strains of S. enterica
subspecies I are present in warm-blooded animals,
while subspecies II, IIIa, IIIb, IV, and VI and S.
bongori are found in cold-blooded animals or in the
environment.
There are approximately 2,500
Salmonella serotypes.
Salmonella grows at
temperatures in the range 5.2-46.2°C but prefers 3543°C. The pH range allowing growth is 3.8-9.5 with
its optimum at 6.5-7.5, while the minimum aw is at
0.93 (ICMSF, 1996; Bacon and Sofos, 2003).
Salmonellosis is caused after ingestion of
contaminated food or water, or through contact with
animals or infected humans. The organism is widely
distributed in the environment, while foods involved
in human illness included animal products, such as
beef, pork, poultry, eggs, raw milk and milk
products; however, salmonellosis has also been
associated with many other foods, including fruits,
vegetables, and dry foods. The blood infection
known as typhoid fever has been virtually eradicated
in the United States, but it may be a more important
problem in developing countries (Blaser et al., 1995;
ICMSF, 1996).
The incubation period of nontyphoidal Salmonella
strains is 5 h to 5 days, and the symptoms of the
infection include diarrhea, nausea, mild fever, chills,
vomiting and abdominal cramps. The duration of the
symptoms is 1-2 days, but may last longer. The
infectious dose in foods may be even as low as 10100 cells, depending on serotype, vehicle of
transmission, and the immune state of the individual
(Blaser et al., 1995; Bacon and Sofos, 2003).
The pathogen invades, multiplies and colonizes the
lumen of the small intestine, and enters the intestinal
columnar epithelial and M cells overlying Peyer’s
patches.
It releases a thermolabile protein
enterotoxin in the cytoplasm of host cells and
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Proceedings, The 15th Congress of FAVA
FAVA -OIE Joint Symposium on Emerging Diseases
27-30 October
Bangkok, Thailand
should yield enough enterotoxin for development of
symptoms. Although staphylococcal food poisoning
can be caused by as little as <10 ng enterotoxin,
levels found in outbreaks may be in the range 1-5 µg
(Mossel et al., 1995; Bacon and Sofos, 2003; Doyle
and Beuchat, 2007).
described as producing two enterotoxins resulting in
watery diarrhea observed before the onset of
dysentery (Bacon and Sofos, 2003).
Staphylococcus aureus
Staphylococci were first recognized as involved in
foodborne illness in 1884. In 1914, Staphylococcus
aureus illness symptoms were observed in
individuals following ingestion of milk. In the
United States, S. aureus is estimated to cause
185,000 cases of foodborne disease annually with a
case fatality rate of 0.0002 (Mead et al., 1999).
The cells are nonmotile, Gram-positive cocci,
occurring singly or in pairs, tetrads, short chains, or
in characteristic “grape-like” clusters. The organism
is facultatively anaerobic, and widespread in the
environment, as it is found on the skin of mammals
and birds, as well as the mouth, blood, mammary
glands, and intestinal, genitourinary and upper
respiratory tracts of infected hosts. S. aureus can
survive for a long time in a dry state, and has been
isolated from air, dust, sewage and water. Foods
involved include ground beef, pork sausage, ground
turkey, salmon steaks, oysters, shrimp, cream pies,
milk and delicatessen salads (Murray et al., 1999;
Lund et al., 2000; Bacon and Sofos, 2003).
Strains of S. aureus grow at 6.1-47.8°C and produce
enterotoxins at 10-46°C; optimum growth occurs at
40-45°C. The organism grows at pH values of 4.09.8, with an optimum between 6.0 and 7.0. It is very
tolerant to salt (>10% sodium chloride), with
enterotoxin production occurring at a minimum aw
of 0.86 (Lund et al., 2000; Bacon and Sofos, 2003).
Staphylococcus aureus causes skin boils, cellulitis,
and postoperative wound infections; it may also
cause bacteremia, pneumonia, osteomyelitis,
cerebritis, meningitis, and abscesses of muscle,
urogenital tract, central nervous system and various
organs. S. aureus may also cause toxic shock
syndrome through production of a toxin (Lund et al.,
2000; Bacon and Sofos, 2003).
Most staphylococcal food poisoning cases may be
traced to food contamination during preparation
followed by inadequate refrigeration, inadequate
cooking or heating, or poor personal hygiene.
Consumption of food containing enterotoxin leads to
symptoms of vomiting, nausea, abdominal cramps,
headache, dizziness, chills, perspiration, general
weakness, muscular cramping and/or prostration,
and diarrhea that may or may not contain blood,
after an incubation period of less than 6 and up to 10
h. Symptoms continue for an average of 26 h, with
mortality rates of 4.4% for children and the elderly
(Bacon and Sofos, 2003; Doyle and Beuchat, 2007).
S. aureus strains produce nine enterotoxins, A, B,
C1, C2, C3, D, E, F and G; types A and D, however,
are responsible for most outbreaks. Enterotoxin A is
more heat sensitive than enterotoxins B or C, as it
requires heating at 80 or 100°C for 180 or 60 sec,
respectively, to cause a loss in serological reactivity.
Growth to more than 105 cells per gram of food
Vibrio cholerae
The etiologic agent of cholera, Vibrio cholerae, was
recognized in 1817 when the first recorded
pandemic occurred.
The organism was first
described in 1854 when it was hypothesized that
there was a connection between cholera and drinking
water, which was proven in 1883 by Robert Koch
who isolated the organism from water. A new
serogroup V. cholerae O139 Bengal was identified
during an epidemic in India in 1992. Other nonO1/O139 serogroups have also been isolated and are
known as nonagglutinating vibrios. According to
estimates, toxigenic V. cholerae are involved in 49
cases of foodborne disease in the United States
annually with a case fatality rate of 0.006 (Mead et
al., 1999; Murray et al., 1999).
As a member of the family Vibrionaceae,
V. cholerae are motile, appear as curved rods and are
common in estuaries. In addition, V. cholerae has
been isolated from freshwater lakes and rivers, and
from birds and herbivores, while V. cholerae O1 is
composed of the classical biogroup that has been
isolated during previous pandemics, and El Tor,
which is the predominant biogroup of the current
pandemic. It has been suggested that the emergence
of V. cholerae O139 Bengal may be the start of the
next pandemic (Murray et al., 1999; Bacon and
Sofos, 2003).
V. cholerae grows optimally at 30-37°C, but growth
can occur between 10 and 43°C. Its optimum pH is
at 7.6, with a range of 5.0 to 9.6, while it requires an
aw of at least 0.97 and prefers 0.984. A sodium
chloride concentration of 0.5% provides optimum
growth, while it can grow at concentrations of 0.1 to
4.0% (ICMSF, 1996; Bacon and Sofos, 2003).
Disease is caused through contaminated food, such
as raw oysters and crustaceans eaten raw,
undercooked or even contaminated following
cooking, or exposure of an open wound to
contaminated water. The infectious dose of
V. cholerae is about 106 cells depending on
buffering capacity of the food. Symptoms range
from asymptomatic to the most severe form known
as cholera gravis. Typical symptoms include muscle
cramps due to dehydration caused by vomiting,
increased peristalsis followed by loose or watery
stools, and mucus-flecked diarrhea. They appear
after an incubation period of several hours to 5 days.
Dehydration is the major complication, while others
may include hypovolemic shock, hypoglycemia and
metabolic acidosis. Noncholera vibrios may cause
self-limiting gastroenteritis and wound infections,
bacteremia and septicemia in individuals with liver
problems (Bacon and Sofos, 2003).
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Proceedings, The 15th Congress of FAVA
FAVA -OIE Joint Symposium on Emerging Diseases
27-30 October
Bangkok, Thailand
been found in the heart, spleen, pancreas and the
liver as they are invasive and can penetrate the
lamina propria and enter circulation (Mossel et al.,
1995; Bacon and Sofos, 2003; Doyle and Beuchat,
2007).
Cholera symptoms are caused by the cholera toxin,
which binds to receptors on the membranes of
intestinal epithelial cells, activates adenylate cyclase,
and produces elevated cAMP levels resulting in the
accumulation of water and electrolytes in the
intestinal lumen. Non-O1 strains do not produce
cholera toxin, but two types of hemolysins and a
heat-stable enterotoxin, and form a capsule that
functions to cause bacteremia, most likely by
blocking the bactericidal activity of the serum
(Bacon and Sofos, 2003).
Vibrio vulnificus
Vibrio vulnificus (Beneckia vulnifica or “lactosepositive Vibrio”) was identified in 1976. Current
estimates indicate that it causes 47 cases of
foodborne disease annually in the United States with
a case fatality rate of 0.39 (Mead et al., 1999; Bacon
and Sofos, 2003).
As a member of Vibrionaceae, the species is motile,
and is found in temperate or tropical, marine or
brackish
waters,
especially
in
estuaries.
V. vulnificus has been isolated from oysters, crabs,
clams, seawater, and intestines of bottom-feeding
fish (Doyle, 1989).
The optimum growth temperature is 37°C, but the
organism can grow in the range 8-43°C. The pH
values allowing growth are in the range 5.0-10.0,
and the minimum aw is 0.96; the optimum values are
7.8 and 0.98, respectively. Growth can occur in
sodium chloride concentrations between 0.5 and
5.0% with an optimum at 2.5% (ICMSF, 1996).
Most cases of V. vulnificus occur between April and
October, when the temperatures are optimal, and are
associated with consumption of contaminated raw
oysters. Compared to other pathogenic Vibrios,
V. vulnificus causes the most severe disease, with
infection of wounds, gastroenteritis and septicemia
occurring rapidly, and frequently resulting in death.
Most (95%) of the deaths caused by seafood in the
United States are due to V. vulnificus. Systemic
infections following oyster consumption occur in
individuals with a preexisting liver or blood related
disorder, such as cirrhosis of the liver, as the
subsequent increase in available iron caused by liver
damage is considered a high risk factor for infection.
Other preexisting risk factors include hematopoietic
disorders, chronic renal disease, gastric disease, the
use of immunosuppressive agents and diabetes; the
infective dose in sensitive individuals may be as low
as 100 cells (Doyle, 1989; Bacon and Sofos, 2003;
Doyle and Beuchat, 2007).
The incubation period is 7 h to several days, and
symptoms may include fever, chills, nausea,
hypotension, abdominal pain, vomiting, diarrhea,
and development of lesions on extremities. The
fatality rate of primary septicemia is 60%, while
wound infections are associated with a 20-25%
fatality rate (Bacon and Sofos, 2003; Doyle and
Beuchat, 2007).
Some pathogenic strains of V. vulnificus produce a
polysaccharide capsule essential for initiation of
infection as it protects the pathogen from
phagocytosis. In addition to the capsule protection,
a serum resistance factor helps to reduce cell lysis.
Vibrio vulnificus are highly invasive and produce a
heat-labile cytolysin that is believed to cause severe
Vibrio parahaemolyticus
The species was first implicated in gastroenteritis in
Japan in 1950, and then in the United States in 1971;
currently, it is considered as an important cause of
diarrhea in the United States and it was associated
with 20 outbreaks in the period 1973-1987, while in
the period 1981-1993, it was responsible for 88
hospitalizations and eight deaths in the state of
Florida (Bacon and Sofos, 2003; Doyle and Beuchat,
2007).
The organism is a member of the family
Vibrionaceae. Thus, it is nonspore-forming, motile,
facultatively anaerobic, Gram-negative straight or
curved rods, and as all pathogenic Vibrio species,
requires sodium for optimum growth. It is found
primarily in brackish or marine environments
located in tropical or temperate areas, as their
incidence decreases significantly as water
temperature falls below 20°C. Foods involved in
illness include crabs, prawns, scallops, seaweed,
oysters and clams. The organism grows at
temperatures between 5 and 44°C, with an optimum
at 30-37°C and a pH of 7.6-8.6, with a range of 4.811.0, sodium chloride concentrations of 0.5-10.0%
and a minimum aw of 0.94; it prefers sodium
chloride levels of 2-4% and an aw of 0.981 (ICMSF,
1996; Murray et al., 1999; Bacon and Sofos, 2003).
Vibrio parahaemolyticus gastroenteritis is usually
associated with consumption of raw, inadequately
cooked, or cooked but recontaminated seafood. The
incubation period is 4-96 h, and symptoms include
nausea, vomiting, headache, abdominal cramps,
slight fever, chills and watery diarrhea, occasionally
bloody. Symptoms after exposure to contaminated
water may include infected wounds, eyes and ears.
The illness is usually self-limiting, lasting only 2-3
days, but severe cases may result in dysentery,
septicemia, cholera-like illness, and death. Preexisting conditions such as liver disease, alcoholism,
diabetes mellitus, and peptic ulcers increase the
likelihood of developing the illness (Lund et al.,
2000; Bacon and Sofos, 2003).
Virulence factors of V. parahaemolyticus include a
thermostable direct hemolysin (TDH), thermolabile
direct
hemolysin,
phospholipase
A,
and
lysophospholipase. Most strains are TDH-negative,
while virulence is related to the presence of the
chromosomal TDH gene and subsequent production
of the enterotoxin. Vibrio parahaemolyticus have
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Proceedings, The 15th Congress of FAVA
FAVA -OIE Joint Symposium on Emerging Diseases
27-30 October
Bangkok, Thailand
The pathogenic serotypes of Y. enterocolitica,
primarily O:3, O:5, O:8 and O:9, produce an
enterotoxin and through the bloodstream they reach
lymphatic tissues, where they proliferate. Yersinia
enterocolitica toxin is heat stable, resists enzymatic
degradation, remains stable during prolonged
storage and is of similar pH stability as the
thermostable enterotoxin produced by ETEC;
however, its toxin may be relatively unimportant in
pathogenesis. Absence of the virulence plasmids or
plasmid function results in inability to cause disease
(ICMSF, 1996; Lund et al., 2000; Bacon and Sofos,
2003).
tissue damage associated with infection.
The
pathogen produces extracellular compounds such as
hemolysin, protease, elastase, collagenase, DNase,
lipase, phospholipase, mucinase, chondroitin
sulfatase, hyaluronidase and fibrinolysin (ICMSF,
1996; Bacon and Sofos, 2003).
Yersinia enterocolitica
The etiologic agent of the plaque, Yersinia pestis,
was isolated in 1894 by Yersin, while the genus
Yersinia was defined by Van Loghem in 1944.
Transmission of Y. enterocolitica to humans through
food was recognized in 1976, even though it was
known as a cause of gastroenteritis since 1965.
Existing estimates in the United States indicate that
Y. enterocolitica is involved in 87,000 cases of
foodborne disease annually, with a case fatality rate
of 0.0005 (Mossel et al., 1995; Mead et al., 1999;
Murray et al., 1999).
The
organism
belongs
to
the
family
Enterobacteriaceae and includes 10 species but only
three are considered pathogenic. Yersinia pestis
causes the plague, Y. pseudotuberculosis is primarily
an animal pathogen, but may infect humans after the
ingestion of contaminated food or water, and
Y. enterocolitica causes foodborne gastroenteritis.
They are Gram-negative, or Gram-variable,
nonspore-forming rods that grow under both aerobic
and anaerobic conditions. With the exception of
Y. pestis, all Yersinia species are motile at 22-30°C,
but not at 37°C (Lund et al., 2000; Bacon and Sofos,
2003).
Yersinia enterocolitica is widely distributed in the
environment and has been isolated from raw milk,
sewage-contaminated water, soil, seafood, humans,
and many warm-blooded animals such as poultry,
and most importantly pigs. It grows at 0-45°C, but
prefers 25-30°C. As a psychrotroph, it may pose a
health hazard in refrigerated foods; however, at
refrigeration temperatures it is usually outgrown by
competing psychrotrophs. Growth occurs at pH 4.010.0, with optimum at pH 7.6. Growth occurs in as
high as 5% sodium chloride (ICMSF, 1996; Lund et
al., 2000; Bacon and Sofos, 2003).
The specific serotypes of Y. enterocolitica involved
in human yersiniosis are prevalent primarily in
swine. Ingestion of contaminated water or food,
mostly raw or undercooked pork, causes infection in
humans. Symptoms appear after a few days to a
week, and may persist for 1-2 weeks in adults and as
long as 4 weeks in children. They include watery,
sometimes bloody, stools or bloody diarrhea in
conjunction with fever, vomiting and abdominal
pain, which may mimic appendicitis and mesenteric
lymphadenitits. Immunocompromised individuals
and children under the age of 15 are most sensitive.
Other syndromes associated with yersiniosis include
septicemia,
meningitis,
Reiter’s
syndrome,
myocarditis, glomerulonephritis, thyroiditis and
erythema nodosum (Lund et al., 2000; Bacon and
Sofos, 2003).
Other Bacterial Pathogens
Additional bacteria may be associated with
foodborne illness, but their involvement is not well
documented. They include Aeromonas, Arcobacter,
other Bacillus species, Brucella, Citrobacter,
Edwardsiella,
Enterobacter,
Helicobacter,
Klebsiella, Mycobacterium, Plesiomonas, Proteus,
Providencia,
Pseudomonas,
Serratia
and
Streptococcus. Important pathogens of current
concern (e.g., E. coli O157:H7, L. monocytogenes,
C. jejuni, Y. enterocolitica, etc.) were unknown or
not officially documented as agents of foodborne
illness until 20-30 years ago and have been
considered as emerging. Epidemiological data and
surveillance estimates by CDC indicate that
approximately 60-70% of the outbreaks and 40-50%
of the cases of reported foodborne illness remain of
unknown etiology (www.cdc.gov). Thus, it should
not be unexpected if additional foodborne pathogens
are identified in the future, as improvements in
microbial detection methodologies are used more
extensively (Bacon and Sofos, 2003; Sofos, 2008).
Aeromonas. The genus Aeromonas belongs to the
family Vibrionaceae, which are Gram-negative,
facultatively anaerobic, primarily motile, rod shaped
organisms. They are found in aqueous environments
and have been implicated in cases of foodborne
illness involving raw meats, poultry, fish, milk and
produce.
They cause infection, resembling a
dysentery-like illness with diarrhea, abdominal pain,
nausea, chills and headache, or an extraintestinal
infection, such as septicemia, meningitis,
endocarditis, peritonitis, endophthalmitis or the
infection of wounds. They grow at 0-45°C, at pH
4.5-9.0, at a minimum aw of 0.95, and at sodium
chloride concentrations of 0.0-4.5% (ICMSF, 1996;
Bacon and Sofos, 2003).
Brucella. Species of the genus Brucella (B. abortus,
B. canis, B. melitensis, B. neotomae, B. ovis, B. suis,
B. maris), are Gram-negative, aerobic, non-motile
cocci or short rods. Human brucellosis is the result
of an infection through handling of infected animals
or of transmission through foods. Brucellosis
involves symptoms such as fever, chills, weakness,
body aches, headaches, sweating, and weight loss.
The organism is aerobic, although some strains grow
best in 5-10% carbon dioxide. Growth occurs at 6S27
Proceedings, The 15th Congress of FAVA
FAVA -OIE Joint Symposium on Emerging Diseases
27-30 October
Bangkok, Thailand
associated with fresh and estuarine water and fish
located in more tropical, temperate environments,
but it has also been isolated from food animals.
Plesiomonas shigelloides typically infect humans
through contaminated water or undercooked
seafood. The incubation period of 24-48 h is
followed by severe abdominal pain, cramps, nausea,
vomiting, fever, headache and dehydration, and may
persist for a period of 2-14 days or longer (Doyle,
1989; Murray et al., 1999; Bacon and Sofos, 2003).
Pseudomonas. Pseudomonads are Gram-negative,
motile, rod shaped aerobes, although some isolates
can grow under anaerobic conditions. They are
found in moist environments including water, soil,
fruits, vegetables, and human gastrointestinal tracts.
The most significant pathogenic species is
P. aeruginosa, with symptoms of skin infection, ear
infection, nosocomial respiratory and urinary tract
infections, and bacteremia. The organism grows at
temperatures ranging from 0 to 42°C, at pH 5.6-9.0,
and in environments with a minimum aw of 0.94
(Doyle, 1989; Murray et al., 1999; Bacon and Sofos,
2003).
Streptococcus. They are Gram-positive,
facultatively anaerobic cocci that colonize the
mucous membranes, and are divided into categories
based on their hemolytic properties, colony size and
responses to Lancefield serological testing. Based
on that, they include S. pyogenes, which following
infection, may induce fever, pharyngitis, respiratory,
skin and soft tissue infections (necrotizing fasciitis),
endocarditis, meningitis, puerperal sepsis and
arthritis; severe infections can lead to shock and
organ failure, a toxic-shock syndrome with 30-70%
mortality. Another species is S. agalactiae, which is
a major cause of mastitis and can be transferred to
humans through raw milk, resulting in sepsis,
meningitis, infant pneumonia, and postpartum
infections. S. pyrogenes possesses virulence traits
that can contribute to infection leading to
bacteremia, endocarditis, meningitis, septic arthritis,
and respiratory tract and skin infections. Finally,
S. milleri strains tend to be less virulent than other
species. Streptococcus can grow at 10-44°C, at pH
values of 4.8-9.2, at a minimum aw of 0.92, and at up
to 6.4% sodium chloride (Doyle, 1989; ICMSF,
1996; Murray et al., 1999; Bacon and Sofos, 2003).
42°C, pH 4.5-8.8, and sodium chloride
concentrations less than 4.0% (ICMSF, 1996;
Murray et al., 1999; Bacon and Sofos, 2003).
Enterobacter sakazakii. The organism was first
recognized as a cause of infant septicemia in 1929,
and in 1961 it was associated with neonatal
meningitis that occurred in 1958. In 1990 it was
associated with infection through consumption of
powdered infant formula. It is considered as a
severe hazard for immunocompromised infants. It
also has been implicated in adult infections. The
organism is considered an important emerging
pathogen. Syndromes associated with the infection
include necrotizing endocarditis, septicemia, and
meningitis. The main source of exposure for infants
is powederd formula in which the organism is
usually present at very low levels (Doyle and
Beuchat, 2007).
Helicobacter. They are Gram-negative spiral or
curved motile bacilli, and as microaerophilic they
grow best in low oxygen levels (5-10%) and
increased amounts of carbon dioxide (5-12%). They
have been isolated from the gastrointestinal tract of
animals and are classified as gastric or enteric,
depending on the primary colonizing site. Gastric
Helicobacter primarily colonize within or beneath
the mucous gel layer next to the epithelium in the
stomach, while enteric strains have been isolated
from blood, and colonize the lower gastrointestinal
tract causing gastroenteritis. H. pylori is the primary
cause of peptic ulcers and it is estimated to infect
50% of the world’s population. Additionally, H.
pylori infection has been associated with a rare
gastric disease known as Menetrier’s disease
(Murray et al., 1999; Bacon and Sofos, 2003).
Mycobacterium. It is the only genus of the family
Mycobacteriaceae, and includes the ‘rapidly
growing’ species which form colonies in less than 7
days, and the ‘slow growing’ which may take six
weeks or more under optimum conditions. The slow
growing species include M. leprae, M. tuberculosis
and M. paratuberculosis. They cause disease in
animals and humans, while, with exceptions, the
faster growing species do not. Mycobacterium are
Gram-positive, nonmotile, straight or slightly
curved, aerobic or microaerophilic bacilli, that grow
best at 30-45°C. Concerns have been expressed
about the potential for food transmission of M.
paratuberculosis, the causative agent of a chronic
infectious ileitis in ruminants known as Johne’s
disease or bovine paratuberculosis. There has been
speculation regarding potential association between
M. paratuberculosis and Crohn’s disease, an
inflammatory bowel disease in humans (Murray et
al., 1999; Lund et al., 2000; Bacon and Sofos,
2003).
Plesiomonas shigelloides. They are Gram-negative,
primarily motile, facultatively anaerobic rods that
have the ability to grow at pH 4.0-8.0, in
environments 0.0-5.0% sodium chloride, and at
temperatures of 8-45°C.
They are primarily
Current Bacterial Food Safety Issues and
Concerns
Microbial infections have been reduced dramatically
since 1900, as there has been progress in sanitary
and hygienic conditions, improvements in methods
of testing and detection, diagnosis and therapy,
progress in immunization, and better food
processing and preservation methods have been
developed and adopted. However, with progress we
have also faced new problems, new diseases, and
new transmission modes such as Legionaire’s
disease, hepatitis C virus, human immunodeficiency
virus, and emerging foodborne pathogens. Current
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FAVA -OIE Joint Symposium on Emerging Diseases
27-30 October
Bangkok, Thailand
climate changes as well as associated natural stresses
which may induce biological changes and lead to
new pathogens; reduction of human populations
directly involved in agriculture; higher numbers of
consumers at-risk for infection; emerging pathogens
that may be resistant to control or more virulent;
advances in microbial detection methods; less food
handling education and training of food handlers and
consumers; increased interest, awareness and
scrutiny of food safety issues by consumers, news
media, and activist groups (Samelis and Sofos,
2003).
An important concern is the development of
antimicrobial resistance in foodborne and clinically
important bacteria potentially due to recent and
current agricultural practices, including use of
antibiotics for therapeutic and nontherapeutic
reasons in animal, plant and aquaculture food
production, as well as their abuse in human
medicine. Concerns include a potential for higher
risk of infection in treated humans; potential failure
of human antibiotics; more severe illness from
resistant pathogens; and potential for co-selection of
higher virulence genes. The issue is complex and
there are no simple solutions. However, it is
recommended to not overuse or abuse antibiotics in
food production and human medicine, prudent use is
recommended, and action should consider individual
situations based on the principles of risk analysis
(IFT, 2006).
Foodborne pathogenic bacteria may also become
resistant to food related stresses such as acid, cold,
heat,
drying,
anaerobiosis,
decontamination
interventions, sanitizers, etc., leading to adaptation
or selection of resistant populations which may
develop multiple resistances or cross-protection to
other stresses (Samelis and Sofos, 2003). Stress
adapted pathogens may be more difficult to control,
leading to failure of preservation systems. This issue
is currently under extensive investigation worldwide
and it is addressed further in following paragraphs.
In addition to the increasing number of pathogenic
agents involved, the number of the types of foods
associated with foodborne illness has also increased.
Examples of food vehicles and associated pathogens
involved in foodborne illness include E. coli
O157:H7 and other hemorrhagic E. coli serotypes
from ground beef, apple juice/cider, other fruit
juices, alfalfa, radish and other types of sprouts,
mayonnaise, watermelon, other produce, jerky and
dry fermented meats; Salmonella from ice cream,
cantaloupes, watermelon, potatoes, alfalfa sprouts,
lettuce, tomatoes, peppers and other produce; S.
Enteritidis from eggs and ice cream; Shigella from
produce; Camplylobacter from poultry and garlic
butter; Y. enterocolitica from chitterlings and tofu;
Y. pseudotuberculosis from milk, pork and possibly
fruit juice; V. vulnificus from oysters; C. botulinum
from potato salad, garlic sauce, sauteed onions,
eggplant, bean dip, clam chowder, olives, summer
sausage, and canned bamboo shoots; L.
and future food safety issues and challenges include:
animal manure and environmental concerns; organic
and natural foods; emerging microbial pathogens;
microbial pathogen control; pathogen resistance and
adaptation
to
stress;
microbial
detection
methodologies; optimal implementation of hazard
analysis critical control point (HACCP); regulatory
modernization and harmonization; food attribution
of microbial disease episodes; and risk-based food
safety objectives (Sofos, 2008).
Newly recognized or emerging foodborne pathogens
in the United States since the 1970s include: C. coli,
C. jejuni, Cryptosporidium parvum, Cyclospora
cayetanensis, E. sakazakii, E. coli O157:H7 and
related E. coli (e.g., O111:NM and O104:H21),
L. monocytogenes, Nitschia pungens (cause of
amnesic shellfish poisoning), Noroviruses, prions,
resistant bacteria, Salmonella serotype Enteritidis,
Salmonella serotype Typhimurium DT 104,
V. cholerae non-O1, V. parahaemolyticus,
V.vulnificus, and Y. enterocolitica. Pathogens of
potential future concern include resistant pathogens
such as Arcobacter, Aeromonas, Plesiomonas,
Escherichia
albertii,
Clostridium
difficile,
Mycobacterium avium subsp. paratuberculosis, and
animal health issues such as avian influenza and
foot-and-mouth disease (Sofos, 2008). Escherichia
albertii consists of Hafnia alvei-like strains,
originally described as Hafnia alvei, which have
caused diarrhea in rabbits through epithelial damage
by attachment and effacement similar to EPEC; it
may also cause HUS, and is related to Shigella
bodyii serotype 13 (Shigella B13). A new more
virulent strain (BI, NAP1, or ribotype O27) of C.
difficile has been involved in antibiotic-associated
diarrhea and colitis. The organism is an important
cause of nosocomial disease in adults, and it is
considered as an emerging pathogen in animals.
Recently, an overlap was found between isolates
from calves and humans, while 20% of retail ground
beef samples were positive (Sofos, 2008).
Reasons for the emergence of new human health
threats include: changes in animal and plant food
production and harvesting procedures, processing
modifications, marketing developments, preparation
practices and development of new food products to
meet consumer demands; increased urbanization and
the associated need for transportation of large
amounts of food products from centralized
production and processing plants to urban centers -food products need a shelf life adequate for
distribution, marketing and consumption in distant
areas; increased international trade and associated
transportation of foods from exporting to importing
countries; globalization of the food industry;
increased travel which may enhance transfer of
pathogens between countries; changing consumer
demographics, lifestyles, eating habits and increased
life expectancy; consumer needs and expectations
for foods that have reduced levels of calories, fat and
additives, while being natural, organic or “healthy”;
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FAVA -OIE Joint Symposium on Emerging Diseases
27-30 October
Bangkok, Thailand
cleaning, sanitation and hygienic activities, and by
application of food product cleaning, washing, and
decontamination
programs.
Destruction
of
contamination is accomplished through cooking,
pasteurization or sterilization (canning) thermal
treatments, as well as nonthermal novel treatments
including irradiation, ultrahigh hydrostatic pressures,
etc. Inhibition of microbial growth is achieved
through cold storage, drying to reduce water activity,
acidification to reduce pH or fermentation to reduce
pH and produce antimicrobials such as acids and
bacteriocins, addition of chemical antimicrobial
agents, and packaging to protect from additional
contamination or modify the gas atmosphere
surrounding the product. Frequently, inhibitory
interventions are applied at sublethal levels in the
form of multiple sequential or simultaneous hurdles
(Koutsoumanis and Sofos, 2004; Koutsoumanis et
al., 2006; Sofos, 2002, 2005, 2006; Stopforth and
Sofos, 2005).
Reasons for pre-harvest pathogen control in the field
include reduction of pathogen sources and levels to
reduce direct animal-to-human transmission of
pathogens, water contamination, and produce or
plant food contamination through animal feces,
manure and contaminated water. Antimicrobial
interventions considered or explored for use in the
field to control contamination on animals include
animal diet modifications, use of feed additives or
supplements, antibiotic treatments, bacteriophage
therapy, vaccination/immunization, competitive
exclusion, prebiotics or probiotics, animal
production management practices such as animal
pen management, clean feed and chlorinated water,
clean and unstressful transportation of animal to
slaughter, clean lairage, and animal cleaning before
slaughter. However, there is no silver bullet; with
the exception of good production and management
practices, and feeding of probiotics, the remaining
approaches are still in the experimental stage or of
limited use (Koutsoumanis and Sofos, 2004;
Koutsoumanis et al., 2006; Sofos, 2002, 2005, 2006;
Stopforth and Sofos, 2006).
For control of bacterial pathogens in fresh raw fruits
and vegetables (produce) the United States Food and
Drug Administration (FDA) has provided two
guides for the industry to follow: “Guide to
Minimize Microbial Contamination of Fresh Fruits
and Vegetables, 1998” and “Guide to Minimize
Microbial Food Safety Hazards of Fresh-cut Fruits
and Vegetables, 2008”. Recommended interventions
are based on well designed and implemented
sanitation programs, worker education, training,
health and hygiene, pest control, appropriate water
quality, and use of chemical or physical
interventions such as washing, chlorine, acidified
sodium chlorite, ozone, electrolyzed water, and their
combinations (Sofos, 2008).
In general, antimicrobial interventions or hurdles
applied for pathogen control in foods include
physical interventions such as low and high
monocytogenes from milk, cheeses, coleslaw, hot
dogs and luncheon meats (Samelis and Sofos, 2003;
www.cdc.org).
Control of Bacterial Foodborne Pathogens
Most foods support growth of microorganisms
associated with spoilage, as well as pathogenic
organisms
leading
to
foodborne
illness
(Koutsoumanis and Sofos, 2004; Koutsoumanis et
al., 2006). Thus, it is necessary to control microbial
contamination in order to prevent foodborne disease.
As indicated, during the early 20th century,
contaminated food, milk, and water caused many
foodborne infections, including typhoid fever,
tuberculosis, botulism, and scarlet fever. As
indicated, a lot of progress has been made in the last
century. Deaths from infectious diseases have
decreased dramatically; life expectancy is longer;
progress has been made in cleanliness and hygiene;
immunization and antibiotic use have helped in
prevention or treatment of disease; food processing
and preservation methods have been discovered,
evolved or been improved; and better methods of
food analysis have been developed. Efforts need to
be continued, however, as additional foods and
pathogens are confirmed as implicated in food safety
problems.
Control of bacterial foodborne hazards and
enhancement of food safety is the responsibility of
all involved in the food chain from farm-to-table,
from producer to packer, processor, distributor,
retailer, foodservice, and consumers. All should be
involved through an integrated approach employing
multiple simultaneous and sequential interventions,
and based on the principles and spirit of the HACCP
system. The target of approaches for control of
pathogens at the pre-harvest level should be to
minimize contamination sources and access or
transfer of contamination to food plants or animals.
During harvest and product processing, the goal
should be to avoid additional or crosscontamination,
remove/reduce
contamination
through washing, sanitization or decontamination
interventions, inactivation of contamination through
heat or other lethal interventions, and inhibition,
delay or retardation of growth in products still
contaminated with pathogens. Control of pathogens
at the foodservice and consumer level should aim at
inhibiting growth, inactivation of contamination
through cooking, and prevention of contamination
transfer or cross-contamination. Additional efforts to
control foodborne diseases involve proper food
labeling, as well as adequate and proper education
and training of food handlers and consumers
(Koutsoumanis and Sofos, 2004; Koutsoumanis et
al., 2006; Sofos, 2002, 2005, 2006; Stopforth and
Sofos, 2005).
The first and most important objective should be
control levels of contamination. This may be
accomplished at the pre-harvest level as well as at
every stage of the food chain through proper
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27-30 October
Bangkok, Thailand
chloride and containing 1% essential oils of
oregano/cinnamon/savory, chitosan-coated films +
nisin / lactate / diacetate / sorbate / benzoate, edible
chitosan film containing lactoferrin or lysozyme or
lysozyme + lactoferrin or nisin, bacteriophages +
nisin, essential oil (thyme) + nisin, high pressure +
nisin or enterocins and/or lactate + diacetate (in
formulation), high pressure processing + active
packaging, high pressure processing + antimicrobial
films (enterocins A and B, sakacin K, nisin A, Klactate, K-lactate + nisin), liquid smoke + postprocess pasteurization, monocaprylin + acetic acid,
nisin and/or lysozyme + in-package pasteurization,
reuterin + nisin / lactoperoxidase system, and
ε-polylysine + nisin.
As indicated, control of pathogenic bacteria in foods
is commonly based on application of more than one
antimicrobial treatment or intervention in the form
of multiple sequential or simultaneous hurdles
(hurdle technology concept; Leistner and Gould,
2002). Presently, implementation of the multiple
hurdle approach is empirical and experience-based.
However, foods and microbes are complex systems
and it is difficult to select proper combinations for
synergistic antimicrobial effects against desirable
targets, which would maximize antimicrobial effects
and product safety. Furthermore, consumers expect
and prefer an adequate food supply that is safe, of
good quality, wholesome, nutritional, and
economically affordable, as well as with no
additives, exposed to minimal processing,
convenient, and safe. However, healthy and
preservative-free foods require mild processing
hurdles. Sublethal hurdles may fail and enhance
stress adaptation, and cross-protection of bacterial
cells. Stressed pathogens may be more difficult to
control, leading to failure of preservation systems.
Therefore, knowledge is needed on mechanisms of
action of antimicrobial hurdles as well as microbial
cell functions, which presently are not well known,
in order to optimize antimicrobial hurdle systems.
Better knowledge of microbial regulatory processes
and hurdle mechanisms will allow optimization of
hurdle application through selection of proper
hurdles which are used at the right intensities or
concentrations, in effective combinations, following
the correct sequence and timing of application in
order to avoid pathogen cell stress adaptation and
resistance development. Instead, proper hurdle
implementation will lead to microbial death through
multiple cell injuries or metabolic exhaustion
(Samelis and Sofos, 2003; Sofos, 2008).
temperature, nonthermal irradiation or high
hydrostatic pressure treatments, and packaging
methods such as modified atmosphere packaging,
including vacuum packaging, high oxygen, low
oxygen,
oxygen-free
controlled atmosphere
packaging, active packaging, smart packaging,
edible packaging films, etc. Physicochemical hurdles
include acidity or low pH, low water activity,
modified oxidation reduction or redox potential (Eh),
and application of chemical antimicrobial agents as
food formulation ingredients or externally applied
solutions or preparations. Biological interventions
include introduction of starter cultures as microbial
competitors (lactics) or as antimicrobial preparations
(bacteriocins such as nisin). Non-thermal novel
processing technologies include ionizing radiation
(gamma, electron beam), high hydrostatic pressure,
pulsed electric fields, sonication, ultrasonic waves,
ultraviolet light, pulsed UV-light, microwaves,
biological or active antimicrobial packaging,
coatings and antimicrobial edible films, and
combinations
of
treatments
or
processes
(Koutsoumanis and Sofos, 2004; Koutsoumanis et
al., 2006).
Recently, common interventions applied to reduce
initial contamination levels on raw foods
(decontamination) include water washing, thermal
treatments such as blanching, hot water
pasteurization and steam treatments, chemical
treatments (organic acids, acidified sodium chlorite,
etc), non-thermal treatments (irradiation, high
pressure), and combinations of these as multiple
hurdles. A brief review of recent scientific literature
indicated that numerous published studies have
evaluated chemical, physical, biological, nonthermal
and combination treatments for pathogen reduction
and control in fresh meat and processed meat
products, and in fruits and vegetables with variable
results. They include: acids (lactic, acetic, citric,
peroxyacetic,
octanoic,
oxyoctanoic,
1hydroxyethylidene-1-diphosphoric),
chlorine
(hypochlorite; chlorine dioxide, aqueous or
gaseous), acidic calcium sulfate, acidified sodium
chlorite, trisodium phosphate, electrolyzed oxidizing
water, hydrogen peroxide, calcium hydroxide, ozone
(aqueous/gaseous), potassium sorbate, sodium
benzoate, sodium bisulfate, sodium lauryl sulfate,
cetylpyridinium chloride, lauricidin, activated
lactoferrin, bacteriocins (nisin, pediocin, colicin E1,
enterocin), bacteriophages, essential oils, chlorine
dioxide (aqueous) + ultrasonication, hot water +
gaseous ozone, ozone + chlorine, ozone (gaseous;
supplied with CO gas), ozone (aqueous) + organic
acids, grapefruit seed extract + nisin + citric acid,
high-intensity pulsed electric fields + citric acid,
hydrogen peroxide + nisin + lactate + citric acid,
titanium dioxide/UV photocatalytic reaction,
ultraviolet light + hydrogen peroxide, edible alginate
coating + essential oils and malic acid, edible yam
starch coating + chitosan, alginate films with
essential oils, alginate films treated with calcium
Implications and Future Outlook
It is natural for raw foods to be contaminated with
microorganisms,
including
pathogens.
Contamination is introduced during production in
the field, harvesting, storage, distribution, further
processing, retailing, preparation and consumption,
and it originates from soil, decaying material, and
animal fecal waste, which contaminate water, air,
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FAVA -OIE Joint Symposium on Emerging Diseases
27-30 October
Bangkok, Thailand
subsequent parts of the food chain will result in
foodborne illness; it will result in products meeting
regulatory standards and commercial criteria and
specifications, respectively, including zero tolerance
requirements for pathogens such as E. coli O157:H7
and L. monocytogenes; products consumed raw or
without further processing for pathogen destruction
will be safer; processes designed to inactivate target
populations of pathogens will not fail due to
excessive initial contamination levels; it will
contribute to meeting pathogen reduction goals set
by regulatory and public health agencies; it will
minimize risks from pathogens of high infectious
dose and will improve the safety of products
contaminated with pathogens of low infectious
doses; it will minimize cross-contamination risks at
all stages of food processing including preparation
for consumption and serving; etc (Koutsoumanis and
Sofos, 2004; Koutsoumanis et al., 2006; Sofos,
2002, 2005, 2006; Stopforth and Sofos, 2005).
In recent years, increased emphasis has been placed
on microbial testing and detection of pathogenic
contamination, even though HACCP was introduced
as means of better pathogen control than spot testing
of finished products. This extensive reliance on
testing has demonstrated the need for development
of better and faster pathogen detection
methodologies for laboratory and field use.
Certainly, this is a worthwile effort because
availability of better detection methods will enhance
identification of pathogen sources and niches, and
contribute to the evaluation and validation of
antimicrobial interventions. Microbial testing is also
necessary in development, validation and
verification of critical control points and critical
limits for inclusion in HACCP programs. However,
it is important to note that microbial testing should
not be considered as a routine method of HACCP
monitoring or as a final step in food safety assurance
(ICMSF, 2002; Sofos, 2008).
With expansion in international food trade, safety
related process management and regulatory activities
and requirements need to be better harmonized.
National
and
international
agencies
and
organizations such as World Health Organization
(WHO), Food and Agriculture Organization (FAO),
World Organization for Animal Health (OIE),
Codex Alimentarious Commission (Codex), World
Trade Organization (WTO), and International
Commission on Microbiological Specifications for
Foods (ICMSF) need to determine responsibilities
for zoonotic diseases and animal health issues.
Harmonization of activities will optimize use of
resources, facilitate trade, eliminate friction, and
enhance food safety (Sofos, 2008).
There is a need for better attribution of foodborne
illness, not only to the responsible etiologic agent,
but also to the responsible food vehicle or other
source. Efforts are being made by the CDC in the
United States to better track foodborne illnesses
through intensified surveillance and epidemiological
animals, plants, processing facilities, equipment, and
humans; leading to a complete contamination cycle.
Pathogen control at the pre-harvest level is difficult
because knowledge is still limited relative to
pathogen reservoirs, methodology limitations,
ubiquitous presence of some pathogens, numerous
and complicating variables involved, and economic
issues. Although it is impossible to produce food
products of animal or plant origin free of
contamination, efforts should continue to minimize
levels of microbial pathogens on raw foods, and to
control contamination through inhibition of growth
or destruction (Sofos, 2004a,b). Reduction of
pathogen prevalence on animals pre-harvest may
lead to a reduced probability that errors occurring in
subsequent parts of the food chain will lead to
foodborne illness.
Decontamination processes are applied on animals,
carcasses, and raw fruits and vegetables and include
animal cleaning, chemical dehairing at slaughter,
spot-cleaning of carcasses before evisceration by
knife-trimming or steam and vacuum, spraying,
rinsing, or deluging of carcasses before evisceration
and/or before chilling with steam, hot water or
chemical solutions (e.g., organic acids, acidified
sodium chlorite, trisodium phosphate, etc.). The fruit
and vegetable industries are also employing
contamination reduction interventions, including
washing with water or chemical solutions (chlorine,
ozone, electrolyzed water, etc.) and thermal
treatments. Additional interventions to help in
enhancing food safety are applied during processing
and include heating, chilling, freezing, drying,
fermentation, use of chemicals as acidulants or
antimicrobials, packaging, proper storage and
distribution, and appropriate handling and
preparation for consumption. Indeed, food safety
assurance involves activities and responsibilities
throughout the food chain. However, reliance only
on controls applied at the final stage of product
preparation for consumption may not be always
effective. Contamination control efforts should be in
place even early in food production in order for
subsequent food processes to be effective
(Koutsoumanis and Sofos, 2004; Koutsoumanis et
al., 2006; Sofos, 2002, 2005, 2006; Stopforth and
Sofos, 2005).
In general, every effort should be made to control
contamination in raw foods, irrespective of further
processing before consumption. Raw foods should
have contamination levels as low as possible. This
may be accomplished through proper production,
sanitation
and
decontamination
practices.
Contamination should then be kept low at all stages
of the food processing chain including packing,
processing, distribution, storage, retailing, etc.
Reduction of pathogen prevalence on animals and
plants pre-harvest and on raw products of plants and
animal origin is beneficial because it should lead to a
reduced probability that food handling, processing
and preparation errors that may occur during
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FAVA -OIE Joint Symposium on Emerging Diseases
27-30 October
Bangkok, Thailand
require complete education and training of business
management and employees. They should know the
objectives and function of HACCP, the need for
proper and continuous application of its principles,
and the importance of controlling foodborne
hazards. SOPs should be simple in language in order
to be understandable by workers. Factory
management should be able to realize the value of
HACCP and the importance of SOPs in order to
provide materials, equipment, and adequate time for
training and education of employees. It is important
to realize that HACCP implementation is not
adequate until there is effective SOP-based training
(Sofos, 2008).
Factors contributing to foodborne illness episodes
include storage of food at inappropriate
temperatures, poor personal hygiene of food
workers, inadequate cooking, contaminated utensils,
and food from unsafe sources (www.cdc.gov). Thus,
human errors lead to most foodborne illness events.
Therefore, there is a need for intensive efforts to
educate food-handlers and consumers in food safety
principles. Specifically, it is important to teach
consumers the basics of proper cooking of animal
foods, thorough washing of raw vegetables,
separation of uncooked from ready-to-eat foods, and
washing of hands, cutting boards, knives, etc, while
individuals at high risk for foodborne illness should
be instructed to avoid or cook risky foods, and to
avoid raw or unpasteurized foods (Sofos, 2008).
Overall, the microbiological status of foods that
reach consumers, either as raw meat or produce or
processed products depends on extent of exposure to
contamination and its control during all steps of the
food production, processing, distribution, storage,
retailing and preparation for consumption chain. For
improved food safety, there is a need to: maintain
contamination levels in unprocessed food as low as
possible; minimize access of microorganisms to
products (live animal, carcasses, fruits, vegetables);
reduce contamination on raw products; inactivate
microorganisms on products without crosscontamination; prevent or inhibit growth of
microorganisms which have gained access to the
meat and have not been inactivated; and properly
cook or prepare products for consumption.
and molecular investigations conducted by FoodNet
and PulseNet. These efforts need to be expanded
nationally and internationally in order to collect
information for better specific food attribution data.
Thus, we will be able to better determine linkages
between changes in foodborne illness estimates and
regulatory and industrial pathogen control activities
in specific segments of the food industry. This
knowledge will provide a better understanding of the
extent of the food safety problem and its causes,
progress in control, and potential risks and new
challenges (Sofos, 2008).
Concerns associated with contamination of the
environment with fecal contaminants from food
animals and wildlife have intensified in recent years,
especially as foods of plant origin, such as lettuce,
spinach, tomatoes, onions and peppers, as well as
potable water, become frequently involved in
outbreaks of bacterial pathogens such as E. coli
O157:H7, Salmonella and Shigella. The impact of
food and wild animals on environmental, water and
food contamination with bacterial pathogens through
microbes present in manure needs careful
consideration as problems may intensify in the
future (Sofos, 2008).
In recent years, microbial risk assessments are
gaining acceptance for application in microbial food
safety, as several of them have been undertaken by
individual scientists, national agencies and
international organizations such as WHO/FAO.
Major, among these, are the draft E. coli O157
ground beef risk assessment of the United States
Food Safety and Inspection service (FSIS), which
was reviewed by a committee of the United States
National Acdemy of Sciences, the WHO/FAO
broiler risk assessment, and the United States
listeriosis risk assessment conducted by FDA, FSIS
and CDC (Doyle et al., 2002; FDA/FSIS, 2003). As
data become available to fill identified gaps, food
safety related risk assessments will improve and help
in the establishment of better hazard control
measures based on performance, process and
product criteria that lead to feasible food safety
objectives (ICMSF, 2002). The goal should be to
base future food safety regulations on the findings of
risk assessments in order to improve international
cooperation, collaboration and harmonization, and
control of foodborne hazards (Sofos, 2008).
The concept of HACCP has become the
international standard for management of food
safety activities worldwide (NACMCF, 1998). Its
success, however, depends on the existence of a
solid foundation of good manufacturing/hygienic
practices and prerequisite programs. Proper and
effective implementation of HACCP also needs to
be based on specific standard operating procedures
(SOP) or job instructions. SOPs should describe the
job to be done, by whom, when, why and how, and
should also provide guidance as to what to do in
case of a deviation (Sofos, 2008). Complete and
effective implementation of HACCP will also
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Bangkok, Thailand
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