Download Foodborne pathogens

Foodborne pathogens
Bacterial agents of foodborne
illness
Food safety
Aeromonas hydrophila
• Foodborne pathogen of emerging importance
• Ability to grow at chill temperatures
• Isolation from patients with diarrhoea / high infection
dose (5x1010) 2 cases from 50 volunteers
• Gram/negative, catalase positive, oxidase positive rods,
ferment glucose
• Optimal T for growth – 28oC
• Fresh food :fish, meat, poultry, raw milk salad
vegetables, water
Bacillus cereus
• Gram-positive, aerobic, spore-forming rods. The genus
contains 80 species
• Grows from 8 to 55oC, optimally 28 - 35oC, spores are
central
• Diarrhoeal syndrome + abdominal pain, nausea and
vomiting less frequent. Onset of illness 8-16h after
consumption of food
• Infective dose – 105 - 107 CFU total
• Association with food: cereals, flour, rice, pasta dishesChinese restaurant syndrome
Bacillus cereus
Campylobacter
• Non-sporeforming, oxidase positive, Gram-negative rods
• Cannot ferment or oxodize sugars
• Oxygen-sensitive microaerophiles, growing best in
atmosphere of 5-10% carbon dioxide and 3-5% oxygen
• All campylobacters grow at 37oC
• C. jejuni + C. coli optimum at 42-45oC, do not grow
below 30oC
• Principal environmental reservoir: alimentary tract of wild
and domestical animals and birds, also found in rodents,
dogs, cats, dairy cattle, sheep, pigs and wild birds.
Campylobacter
• Cause acute enterocolitis, not easily distinguished
fromillness caused by other pathogens.
• Incubation period 1 to 11 days, usually 3 – 5 days
• Fever, severe abdominal pain and diarrhoea
• Excretion of organism continues 2 – 3 weeks
• Complications – in rare cases neurological disease
Guillain-Barre syndrome
• Low infectious dose
• In 2007 leading cause of infectious diarrhoea in Europe
Campylobacter jejuni
Campylobacter
Clostridium botulinum
• First report about toxin from 1793 “Wurstvergiftung”
botulus = sausage
• In 1896 isolated and described by van Ermengem
• Gram-positive rods, motile with peritrichous flagella,
obligately anaerobic , central spores, production of
neurotoxins – eight types: A, B, C1, C2, D, E, F, G
• Single strain of C.botulinum produce one type
• Generally psycrotrophic from 3 – 15oC
• Three types of botulism are recognised: foodborne
botulism, infant or infectious botulism and wound
botulism
Clostridium botulinum
• Foodborne botulism is an example of bacterial food
poisoning in its strictest sense:it results from the
ingestion of an exotoxin produced by Clostridium
botulinum growing in the food.
• Symptoms of botulism occur from 8h to 8 days, most
commonly 12-48 h, after consumption of the
toxin/containing food.
• Vomiting, constipation, double vision, difficulty in
swallowing, dry mouth, difficulty in speaking
• Neuromuscular blockade antagonist, 4-aminopyridine
• Survival critically dependent on early diagnosis +
treatment, mortality 20-50%, type of toxin dependent
Clostridium botulinum
• Low-acid canned foods, home-canning (vegetable +
meat), duck pate, minced meat pie etc.
• Infant botulism differs from the classical syndrome /
result of colonization of the infants gut with C. botulinum
and production of toxin in situ.
• Mostly in infants from 2 weeks to 6 months
• Wound botulism – subcutaneous infection with C.
botulinum. Result of trauma or alsou intravenous drug
use
• Isolation and identification - long protocol using mice
Clostridium botulinum
Clostridium perfringens
• Cause of food poisoning – five types of exotoxin,
• Self-limiting, non/febrile illness nausea, abdominal pain,
diarrhoea less commonly vomiting
• Onset usually 8 to 24 h after consumption of food with
large number of vegetative organism
• Ingested vegetative coells that survive stomach`s acidity
pass to the small intestine, grow, sporulate and release
an enterotoxin
• Enterotoxin is produced by sporulating cells
• Toxin is 35 kDa protein – inactivated by 10min heating at
60oC
Clostridium perfringens
• Typical scenario of food poisoning: a meat dish
containing spores of C. perfringens is cooked,
• The spores survive the cooking to find themselves in a
genial environment without any competing microflora
• After cooking, the product is subjected to temperature/
time abuse, such as slow cooling or prolongaated
storage at room T. This allow the spores to germinate
and mutiply rapidly to produce a large vegetative
population.
• The product is either served cold or reheated
insufficiently to kill vegetative cells.
• Most outbreaks: institutional catering(schools, hospitals)
Enterobacter sakazakii
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Foodborne pathogen of emerging importance
Threatening infections in low birth-weight infants
First cases in 1958
Up to 2005 75 cases of Ent.sakazakii infection worlwide
Gram-negative, motile member of the
Enterobacteriaceae
Typical mesophil, growth between 6o - 47oC
Heat resistance varies between strains
Powder infant formula foods, water, soil, tofu
Cronobacter ?
Enterobacter sakazakii
• Electron microscopy picture
Escherichia coli
• Universal inhabitant of the gut of humans and other
warm/blooded animals - predominat facultative anaerobe
• Generally a harmless commensal
• Opportunistic pathogen causing infections such as
Gram-negative sepsis, urinary tract infections,
pneumonia in immunosuppressed patients and
meningitis in neonates
• It is a catalase-positive, oxidase-negative, fermentative,
short,gram-negative, non–spore-forming, usually with
flagellae that are peritrichous, and fimbriate bacillus
Escherichia coli
Escherichia coli
Enterotoxigenic (ETEC),
Enteroinvasive (EIEC),
Enteropathogenic (EPEC),
Enterohemorrhagic (EHEC),
Enteroaggregative (EaggEC),
Adherent E. coli (DAEC)
Enterotoxigenic
E. coli
• ETEC are a common cause of infectious diarrhea
(Black, 1993), especially in tropical climates.
• Illness occurs between 12 and 36 h after ingestion
of organism.
• ETEC produces a watery diarrhea associated with
cramps and a low-grade or no fever, vomitting.
• The illness is self-limiting, persisting for 2 or 3 days
• It is a common a cause of infantile diarrhea where it
can cause serious dehydration.
• Diarrhea caused by ETEC has a lot in common with
cholera; both result from ingestion of rather large
inocula of bacteria, which then colonize the small
intestine and produce toxins that cause net
secretion into intestinal lumen.
Enteroinvasive
E. coli
• EIEC- classic symptoms of an invasive bacillary
dysentery / normally Shigella
• EIEC invades and multiplies within the epithelial cell of
colon causing ulceration and inflammation
• EIEC strains do not produce Shiga toxin
• Invasiveness is detremined by a number of outer
membrane proteins, coded by large plasmid ( 140 Mda)
Enteropathogenic
E. coli
• EPEC infection usually results in watery diarrhea
accompanied by vomiting and fever, but in some cases
there is prolonged chronic enteritis.
• Disease appears 12-36 h after ingestion of the organism.
• EPEC is traditionally associated with outbreaks in
maternity units and child daycare centers, although
outbreaks in adults are also common.
• In infants, the illness is more severe than many other
diarrheal infections can persist for longer than 2 weeks in
some cases.
Enterohemorrhagic
E. coli
• The EHEC group causes severe bloody diarrhea
(hemorrhagic colitis), hemolytic uremic syndrome
(HUS), and thrombotic thrombocytopenic purpura.
• Although sometimes the infection causes only
diarrhea or no symptoms.
• The EHEC strain most commonly found is
O157:H7.
• EHEC strains produce cytotoxin Verotoxin
(so/called because of its ability to kill Vero African Green Monkey Kidney cells
Listeria monocytogenes
• L.monocytogenes is the only important human
pathogen among the six species currently recognized
within the genus Listeria, although L. seeligeri, L.
welshimeri and L.ivanovii occasionally cause human
infections.
• L.monocytogenes is a Gram-positive , facultatively
anaerobic, catalase-positive, oxidase-negative, nonsporeformer.
• L.monocytogenes elaborates a 58 kDa β-haemolysin,
listeriolysin O, which acts synergistically with the
haemolysin produced by Staphylococcus aureus
L.monocytogenes
morphology
Listeria monocytogenes
Scanning EM showing Flagella
L.monocytogenes
• Organism grows over a wide range of temperature from
0 – 42oC with an optimum between 30 and 35oC .
• Organism is ubiquitous in the environment. Isolation from
fresh and salt water, soil, sewage sludge, decaying
vegetation, silage.
• Oportunistic pathogen – incubation periods for disease
from 1 day to 90 days. Symptoms vary from a mild, flulike illness to mengitis and meningoencephalitis.
• Attack : pregnant women, very young (0 – 2 years) or
elderly (more 65 years) and the immunocompromised
population.
L.monocytogenes
• Association with food : documented were: coleslaw
salad, raw vegetable (celery, tomatoes, lettuce), dairy
products as raw milk, soft cheeses, smoked salmon,
pork tongue in aspic.
• Ability to multiply at refrigerator temperatures
• Morrtality: 20 – 40%
Mycobacterium species
• Genus Mycobacterium largely harmless environmental organisms
but is best known as the cause of two of the most feared and
ancient of human diseases, tuberculosis (TB) and leprosy.
• Human illness is associated with Mycobacterium tuberculosis.
Also causes tuberculosis in cattle and other animals.
• Organism is Gram-positive, non-sporeforming pleomorphic aerobes
with special composition of cell wall. High lipid content made up of
esterified mycolic acids, complex branched-chain, hydroxy lipids
resulting in very hydrophobic and waxy surface
• Milk was main food source
Plesiomonas shigelloides
• Isolated in tropic countries – belongs to
Enterobacteriacae – Gram-negative, catalase –positive ,
oxidase-positive rod.
• Temperature range from 8-10oC to 40-45oC , ubiquitous
in surface water an soil.
• Associationwith food : fish and shellfish (crab, shrimp,
oysters)
• Diarrhoea in the absence of fever
Salmonella
Gram-negative, non-sporeforming rods, member
of Enterobacteriacae, facultatively anaerobic,
catalase-positive, oxidase-negative, generally
motile,
minimum aw 0.93, survive in dry foods
Salmonella
Salmonella
Serotyping scheme :Kaufmann and White more
than 2000.
Salmonella - growth on XLD agar
Salmonella - pathogenesis
• Salmonellas are responsible for a number of different
clinical syndromes grouped as enteritis and systemic
disease.
• Enteritis – gastrointestinal infections of different
severity, about 200 serotypes are associated with human
illnesses. S. Enteritidis, S. Typhimurium, S. Infantis,
• Incubation period is typically 6 to 48 h.
• Principal symptoms, mild fever, nausea, vomiting,
abdominal pain and diarrhoea, last few days, may persist
a week or more
• Illness is self limiting
Salmonella - pathogenesis
• Systemic disease, host-adapted serotypes are more invasive and
tend to cause systemic disease in their hosts. S.Typhi, S.Paratyphi
A,B and C.
• Typhoid fever has incubation period from 3 to 56 days, usually
between10 and 20 days.
• Invasive salmonellas penetrate the intestinal epithelium and are
then carried by the lymphatics to the mesentheric lymph nodes.
After multiplication in the macrophages, they are released to
drain the blood stream, and disseminate around the body.
• They are removed from the blood by macrophages but continue to
multiply within them. This kills the macrophages which then release
large numbers of bacteria into the blood causing septicaemia.
Macrophage infected by S.tyhimurium gfp labelled in
promotor region. Extracelullar microbes are stained by
antibody conjugated with fycoerythrin (red).
Salmonella - pathogenesis
• In this , the first phase of the illness, the organism may be cultured
from the blood.
• Slow onset of symptoms: fever. Headache, abdominal tenderness
and constipation.
• During the second stage of the illness, the organism reaches the
gall bladder wher it multiplies in the bile.
• The flow of infected bile reinfects the small intestine causing
inflammation and ulceration. Fever persists with onset of diarrhoea
in which large numbers of bacteria are excreted with the
characteristic”pea soup” stools.
• This infectionis treated with antibiotics (chloramphenicol,
ampicillin and amoxycillin.)
• After remission of symptoms , a carrier state can persist for several
months (years) and bacteria are discharged intermittently with the
bile into faeces.
Salmonella - pathogenesis
• Nowadays chronic carriers can be treated with
antibiotics
• Recalcitrant cases – cholecystectomy (surgical
removal of the gall bladder) is necessary.
• People bearing sallmonella – prohibition of work in
food industry and distribution.
• Association with food: zoonotic infection, major source of
human illnessis infected animal.
• Transmission = faecal – oral route
• Meat, milk, poultry, eggs – p[rimary vehicles
• Cross-contamination via kitchen equipment or by contact
Salmonella / serotypes
• Salmonella Enteritidis PT4 (phage type) prevailing type
• Massive increase in salmonella infection started in
1985
• Biosecurity measures to exclude salmonella and reduce
the number of infectionon egg and poultry farms.
• Compulsory bacteriological monitoring of all commericial
egg-laying and breeding flocks ( Denmark,UK, Germany)
• In 2005 EU average 20.3%, UK 8%, Norway, Sweden,
and Luxembourg 0%, Spain, Poland, Czech Republic
50%
Shigella
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Shigella dysenteriae
Shigella flexneri
Shigella boydii
Shigella sonnei
All are human pathogens causing bacillar dysentery,
DNA relatedness show close relation to Escherichia
Family Enterobacteriaceae – Gram-negative, non-motile
rods, catalase positive, oxidase negative , facultative
anaerobs
• Typical mesophiles, 10 – 45oC, pH range 6 - 8
Association with food
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Primary source – sewage - vegetable (iceberg lettuce)
Uncooked foods ( prawn coctail, tuna salad)
Infection dose is low, 10 – 100 organisms
Incubation period vary from 7h to 7days
Symptoms – abdominal pain, vomiting, fever, diarrhoea,
with bloody stools
• Illness lasts from 3 days up to 14 days
• Carrier state may develop – persistence for several
months
Staphylococcus aureus
In 1882 name
staphylococcus , Greek
staphyle = bunch of
grapes,
coccus = a grain or
berry
Staphylococcus aureus
• Food poisoning agent
• Currently 27 species and 7 subspecies of the genus
Staphylococcus
• Enterotoxin production principally associated with the
species Staph.aureus
• Relatively mild, short-lived type of illness
• Staphylococcal food poisoning is perhaps underreported
• Staph.aureus Gram-positive coccus forming spherical to
ovoid cells, 1 μm in diameter
• Catalase-positive, oxidase-negative, facultative
anaerobs
Staphylococcus aureus
• Typical mesophile 7 – 48oC, pH range 6 – 7
• Organism has unexceptional heat resistance with high D
value
• Tolerant to salt and reduced aw
• Grows readily in media with 5-7% NaCl, some strains up
to 20%.
• Food poisoning by Staph. aureus short incubation
period, typically 2-4 h. Nausea, vomiting, stomach
cramps, retching are main syndroms. In severe cases
dehydration, marked pallor and colapse.
Staphylococcus aureus
• Illness is a result of ingestion of a pre-formed toxin in
the food.
• Staph. aureus produces at least 11 enterotoxins
designated SEA to SEJ. SEC – 3 variants, No SEF.
• Toxins types A and D, either singly or in combination,
are most frequently implicated in outbreaks of food
poisoning.
• Though described as enterotoxins the Staph. aureus
toxins are strictly neurotoxins.
• They elicit the emetic response by acting on receptors in
the gut, which stimulate the vomiting centre in the brain
via the vagus and symphatetic nerves.
Staphylococcus aureus
• A number of immunoasay techniques for
staphylococcal enterotoxins are available
• ELISA techniques detect 0.1 – 1.0 ng toxin g-1 food
• Reverse passive agllutination tests 0.5 ng ml-1
• It will occur naturally in poultry and other raw meats
• Skin microflora, also raw milk, dry milk
• Hard cheeses, cold sweets, custards, creamy-filled
bakery products
• In Japan - rice balls moulded by hand
• In Hungary – ice cream
Vibrio
• Historically, cholera has been one of the disease most
feared by mankind.
• Still endemic to the Indian subcontinent, during 19th
century several pandemics of “Asiatic chelera” in Europe
and Americas.
• Vibrio cholerae Gram-negative pleomorphic (curved or
straight) short rods, motile with shethed polar flagella.
• Catalase and oxidase-positive, facultative anaerobs,
tolerant to 3% NaCl, temperature range from 5 - 43oC,
optimum 37oC.
Vibrio
• Cholera has an incubation period from one to three days.
• Illness vary from mild, self-limiting diarrhoea to a severe
life-threatening disorder
• Infectious dose in healthy individuals is large – 1010 cells.
• Pathogenicity is strongly linked to formation of 22 kDa
thermostable extracelluar haemolysin.
• Cholera is regarded as a water-borne infection, though
food which was in contact with contminated water is also
vehicle.
• Sea food, shellfish, oysters etc.
Yersinia enterocolitica
• Yersinia enterocolitica is one of the three species of the
genus Yersinia recognized as human pathoges.
• Yersinia enterocolitica causes gastroenteritis
• Yersinia pseudotuberculosis - mesenteric adenitis
• Yersinia pestis – bubonic plague which killed in 14th
century 25% of European population
• Member of the Enterobacteriacae, Gram-negative short
rod, catalase-positive, oxidase-negative. It can grow
from -1 to 40oC, with an optimum about 29oC.
• Y. enterocolitica was isolated from soil, fresh water,
intestinal tract of many animals., dairy products, meat
(pork), fish, poultry fruits and vegetable.
Yersinia enterocolitica
• Illness occure most commonly in children under 7 years
old.
• It is self-limiting enterocolitis with an incubation period of
1 – 11 days and lasting for between 5 – 14 days.
• Symptoms are abdomibnal pain and diarrhoea, mild
fever.
• Pigs are chronic carriers of Y. enterocolitica serotypes
most commonly found in human infections.
Y. enterocolitica on XLD agar plate