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FE- Food Microbiology
Spring 2015
• Introduction
Main characteristics of foodborne
• Type of Foodborne Toxicoinfections
Aeromonas hydrophila
Bacillus cereus
Clostridium perfringens
Clostridium difficile
Plesiomonas shigelloides
Vibrio Cholera (Cholera)
Enterotoxigenic and Enteropathogenic E. coli
Foodborne Toxicoinfection
It is the combination of food intoxication and
infection. The microorganism grows to very high
number in a food and continues its growth in
the intestinal tract and cause ilness.
Generally, toxicoinfections involve either
sporulation or death of bacterial cells and
release toxins in the gastrointestinal tract.
Some characteristics of Foodborne
• For spore formers, ingestion of large numbers of vegetative
cells is required. Vegetative cells do not multiply in the
digestive tract, but some sporulate and release toxins.
• For Gram-negative non spore forming bacteria, the cells can
be ingested in moderate numbers. The cells rapidly multiply
in the intestinal tract and many cells are died and died cells
release toxins
• Toxins o both groups produce gastroenteritis symptoms.
Food borne toxicoinfections are caused by Aeromonas
shigelloides,Vibrio cholerae (Cholera),Enterotoxigenic and
1. Aeromonas hydrophila
Characteristics of organism
• Members of Vibrionaceae family
• Present in salt and freshwater and estaurine water
• Gram negative
• Facultative anearobic
• Catalase and oxidase-positive
• Can be motile and non motile
• Bacilli shaped (1-3.5 µm length) usually presents in
single or short chains
• Mesophilic or psychrophilic.
• Optimum temp. 28 ˚C. It can grow temp range from
5 to 42 ˚C
• İs killed by heating 60 C in 10 min
• It is fairly sensitive to low pH(below 5.5)
• It does not grow at high salt concentration(above
1. Aeromonas hydrophila - Nature and
Food Associations
They present primarily aquatic environment.
Common in sea water, well water, sink water, sewage and
wide range of seafood.
In fresh meat and poultry they are in small numbers but
can increase during storage at chill temperatures
Wide variety of vegetables can contain this organism from
contaminated water
1 Aeromonas hydrophila -Disease and
Can cause wide range of localized , wound and
systemic illnesses.
The symptoms are dependent on bacterium,
Host, inoculum size, and infection site.
The most common infection is gastroenteritis
(infants, children under five years old, elderly and
immunocompromised people)
Infective dose ranges from 104 to 1010 cells.
The main virulence factors associate with the
production adhesions, exotoxins, heat stable and
heat label shigella like toxin, extracellular
enzymes and endotoxins.
1. Aeromonas hydrophila -Prevention
and Control
• Use additional preservation method for foods stored at
low temp( below 5 °C)
• Sufficiently cooking seafoods and disinfection of
drinking water.
• Organic and inorganic acid can be effective.
Polyphosphate and NaNO2 can also control the control
the growth.
• Can be controlled by heat treatment, preventing post
heat contamination and by using one or more growth
limiting factor such as pH ad water activity.
• Are easily destroyed by heating at 56 ˚C for 10 min.
1. Aeromonas hydrophila -Isolation
and Identification
• When low numbers are present , enrichment
media such as alkaline peptone water are used
to increase number of A. hydrophila but when
high numbers direct plating is sufficint.
• Many strains ferment lactose and can not
ferment xylose and these are useful
distinguishing factors in media.
• As well as bile salts , ampicillin is used as a
selective agent in media such as starch ampicillin
agar and blood ampicillin agar.
2. Bacillus cereus
Characteristics of organism
Gram positive
Rod shaped
Motile and areobic
It produces central to term,nal allipsoidal or
cylindrical endosspore and do not cause swelling
in the sporangium
Temp range 10 to 50 ˚C
pH range 4.9-9.3
Salt concentrations below 10%
Due to the spores it can be isolated from soil,
water and vegetables.
Can grow in past. milk and produces a protease to
cause off flavors.
Spores are relatively heat resistant
2. Bacillus cereus - Nature and Food
Widespread in nature and commonly in soil, dust and
growing plants. Meat, eggs, rice, pasta and dairy products
are the most common food vehicles for B. cereus.
this organism from contaminated water
2. Bacillus cereus - Nature and Food
Heat processing will select the spore formers
and a high number of B. cereus spores survive at
pasteurized and other heat processing of foods.
In most of these cases the numbers are low.
When pasteurized milk or cream is stored at
inadequate chill temperatures, B.cereus can
grow and cause spoilage known as ‘’Sweet
Curdling’’ or ‘’bitty cream’’.
2. Bacillus cereus –Foodborne
B. cereus causes two types of food poisoning:
The emetic type
The diarrheal type.
Infectıve dose
Diaarheal syndrome
Emetic syndrome
Toxin produced
In the small intestine
Performed in the food
Type of toxin
Cyclic peptides
Incubation period
18-24 h( approx. 12 h) 1-6 h
Duration of ilness
12-24 h
Abdominal pain,
watery diarrhea
(occasionally bloody
Foods of most frequently Meat products, soups,
associate implicated
and milk products
105-108 cells/g food
8-24 h
Nausea, vomiting,
malaise, diarrhea
Fried and cooked rice,
pasta, pizza, pastry,
2. Bacillus cereus –Prevention and
The important factors in the B. cereus disease are improper
holding temperature, contaminated equipment, inadequate
cooking and poor personal hygiene.
The food should be kept at low or high temperature to
prevent spore germination. Quick chilling of the food to 4 °C
or holding the food above 60 °C can achieve this.
Strict temperature control must be exercised in the cooling
and holding of cooked foods.
The strong adhesion problem of B. cereus can be
overcomed with use of hypochlorite(0.2% at pH 7-8)
2. Bacillus cereus –Isolation and
In outbreaks of B. cereus food poisoning, foods will
contain large numbers (above 105/g) so enrichment
techniques are not required.
Selective agar medium(Bacillus cereus agar)contains
mannitol egg yolk and polymyxin as a selective agent to
suppress Gram negative bacterium. B. cereus can be
identified after 24 h incubation at 35 °C by its
characteristic colonial morphology. Hemolysing producing
B. cereus gives hemolytic colonies. Colonies can be
further confirmed by microscopic procedure with spore
3. Clostridium perfringensCharacteristics of the organism
Gram positive
Large rod shaped (2-4 µm in length)
Spore forming
Swelling the sporangium with spore
Non motile
Catalase negative
It produces H2S
Growth occurs over the temperature range 12-52 °C with optimum 6.0-7.5
The vegetative cells are sensitive to low heat treatment but their spores are
extremely heat resistant and some can survive at boiling temperature for
several hours.
3. Clostridium perfringensCharacteristics of the organism
It is probably the most widespread of all pathogenic
bacteria. There are several toxigenic types :A,B,C,D and E
based on the production of four enterotoxins: alpha,beta,
epsilon and iota.
C. Perfringens type A:produces only alpha toxin
C. Perfringens type B:produces alpha,beta, epsilon C.
Perfringens type C:produces alpha,beta.
C. Perfringens type D:produces alpha, epsilon
C. Perfringens type E:produces alpha and iota
C. Perfringens type A is responisble of food poisoning and
gas gangrene on human.
3. Clostridium perfringens-Nature and
Food Associations
• It is extremely widespread in nature; dust, air and raw
• It is a common inhabitant of the intestinal tract of heathy
animals and human beings.
• Spores of organism can survive at many food processing
• Due to the its ability to grow over a wide temperature
range, it is often implicated in human food poisoning.
• Clostridium perfringens most closely associates with
gangrene and wound infections.
• Foods commonly associating with C. Perfringens are meat,
poultry, fish, shellfish, vegetables, dairy products, eggs and
3. Clostridium perfringens-Disease and
Human food poisoning is caused by the ingestion of food
containing a large number of vegetative cells.
The enterotoxin causes gastroenteritis.
The symptoms appear 8-24 h following ingestion of a large
number of viable cells(about half million cells/g).
Symptoms include diarrhea, abdominal pain, nausea, vomiting
and fever.
The toxin changes the permeability of intestinal cells.
Fatality is rare, but it can occur in very young, elderly and sick.
Symptoms disappear within 24 h.
This disease is considered a mild one.
3. Clostridium perfringens-Disease and
Gas gangrene is a bacterial infection that
produces gas within tissue in gangrene. It is
caused by exotoxin-producing clostridial
species(most often C. perfringens).The exotoxin
is commonly present in C. perfringens type A
species and is known as alpha toxin.
These toxins destroy nearby tissue, generating
gas at the same time.
3. Clostridium perfringens-Prevention
and Control
Proper sanitation in all phases of food preparation
and handling.
Food should be cooked to the highest temperature
recommended to kill the cells and as many spores
as possible.
The food should be cooled quickly and uniformly
To refrigerated temperature.
If a food is stored for a long time, it is important to
reheat it quickly and uniformly and keeping it hot
while being served.
3. Clostridium perfringens-Isolation
and Identification
• Selective agar medium is used in ısolation.
• In the examination of foods, total count for C.
perfringens (vegetative cells plus spores) is determined
with fecal sample, a spore count is obtained after
heating at 80 °C for 10 min.
• The most common selective medium used to
enumerate C. perfringens is perfringens agar and
incubated anaerobically at 35 °C for 24 h.
• Characteristic colonies can be confirmed by the
absence of motility, ability to reduce nitrate to nitrite,
lactose fermentation, gelatin liquefaction and Nagler
4. Clostridium
difficile(pseudomembranous colitis)
• C. difficile causes antibiotic associated
diarrhea(AAD) and more serious intestinal
conditions such as colitis and
pseudomemranous colitis in humans.
• People in good health usually do not get C.
difficile disease and individuals who have
other conditions that require prolonged use of
antibiotics and elderly are at greater risk of
4. Clostridium difficile- symptoms and
• İt produces two toxins: Toxin A is referred to as an
enterotoxin because it causes fluid accumulation
in the bowel. Toxin B is an extremely
lethal(cytopathic) toxin
• Avoid broad spectrum antibiotic use. Probiotics
may be considered in recurrent cases.
• Practice good hygiene(hand washing, disinfect
surfaces such as bleach, alkaline glutaldehyde
and ethylene oxide)
5.Plesiomonas shigelloidesCharacteristics of organism
It is an enteric pathogen and causing foodborne outbreaks.
It present in the family of Plesiomonadeceae
Gram negative
Catalase and oxidase positive
Mesophilic, rod-shaped non-halophilic
It grows temp. Range from 8 to 45 °C with optimum 35 °C,
at pH 5 to 8 but susceptible to low pH.
Aerobic or facultative anaerobic
Non spore forming rod(3.0µm in length) or filamentous
Motile with lophotrichous 2-5 flagella
Produce H2S
5.Plesiomonas shigelloides-Nature and
Food Associations
• Most infections occur in the summer months and
correlate with environmental contamination of
freshwater(rivers, streams, ponds, etc)
• The usual route of transmission of the organism is
by ingestion of contaminated water or uncooked
raw fish and shellfish.
• The most common foods associating with P.
Shigelloides outbreak are oyster, chicken,fish and
5.Plesiomonas shigelloides-Disease
and symptoms
• It can cause wound infections, septicemia and
• The symptoms appear within 24 h following ingestion
of contaminated food or water with viable cells
• Virulence factors of P. shigelloides are extracellular
enzymes(e.g.elastase), heat stable
enterotoxins,cytotoxins,) hemolysin, exotoxin,invasions
(invasion of HeLa cells )and adhesions (glycocalyx)
• P. shigelloides is gastroenteritis is usually a mild selflimiting disease with fever, nausea, abdominal pain,
dehydration, vomitting and chill.
5.Plesiomonas shigelloides-Prevention
and control
• It is killed at pasteurization temperature. Adequately
cooked foods can not contain viable cells and proper
refrigeration controls its growth.
5.Plesiomonas shigelloides-Isolation and
It is an enteric pathogen. Alkaline peptone water and
tetrathionate broth can be used as an enrichment media.
Selective medium used for isolation of organisms is
Plesiomonas agar containing inositol, brillant green and
bile salts.
6.Vibrio cholerae (Cholera)Characteristics of the organisms
• It is a member of family Vibrionaceae
• is a Gram-negative
• motile with monotrichous flagellum,
• comma-shaped, facultative anaerobic.
• Two serogroups of V. cholerae:
01 and 0139 they cause outbreaks but 01 serogroup causes
the majority of cases.
V. Cholerae 01 has 2 biotypes;
Classical and El Tor
Each biotype has three serotypes; Inaba, Ogawa and Hikojima.
Non 01 serotype strains are isolated from coastal waters.
6.Vibrio cholerae (Cholera)Nature and food associations
It is widely distributed in aquatic environments.
Marine environments may serve as long-term reservoirs. Both
serotypes, especially non-01, have been isolated from water.
The disease results from ingestion of infective doses of V.
cholerae( about one million cells) through foods and water
contaminated with feces of humans suffering from the disease
The handling of food by a person suffering from the disease can
also contaminate food, because of poor personal hygiene.
Food originating from natural reservoirs of the causative bacteria
can be contaminated and spread cholera. The natural reservoirs
include marine and brackish water environments.
Among the types of contaminated foods are raw oysters,
Crab, fish and shrimp and cooked rice.
6.Vibrio cholerae (Cholera)Disease and symptoms
• Illness of cholera is due primarily to action of cholera enterotoxin.
• Cholera is a disease characterized by severe, dehydrating diarrhea
• Infectious dose is about 106 cells or more per gram of food.
Incubation period for cholera varies from several h to days.
• Toxin stimulates adenyl cyclase in the intestinal epithelial cells to
produce cyclic AMP which causes massive secretion of water along
with chloride, potassium, and bicarbonate in the lining of the
intestine therefore toxin disrupts ion transport.
• Initially the stool is brown with fecal matter, than becomes a pale
gray color with slightly fish odor; mucus in the stool imparts the
characteristics «rice water» appearance. The symptoms fallow with
the sudden onset of rice watery diarrhea, severe prostration,
painful muscle cramps, clouded mental status, loss of fluids,
dehydration of intestinal cells and circulatory collapse.
6.Vibrio cholerae (Cholera)Prevention
Adopting proper hygienic measures.
Provision of properly treated municipal water.
Decontamination of suspected water by boiling.
Proper disposal of sewage.
Treating of infected persons with antibiotics
along with replacing body fluids.
Vaccination of unexposed people.
Seafoods should not be eaten raw.
6.Vibrio cholerae (Cholera)Isolation and Identification
Isolation of V. cholerae from a sample is
achieved by an initial pre enrichment in alkaline
peptone water, followed by streaking on a
selective agar medium plate such as thiosulfate
citrate bile salt sucrose agar.
Suspected colonies(yellow) are biochemically
and serologically tested for confirmation.
The toxin is detected by immunoassay.
7. a.Enterotoxigenic Escherichia
• Humans are the principle reservoir of enterotoxigenic
E. coli (ETEC) strains that cause human diarrhea.
Human carriers can spread the ETEC strains directly
and indirectly. Foods (such as cheese) and water
associated with human ETEC outbreaks.
• ETEC strains are major cause of diarrhea among
travelers and infants for poor sanitation.
• Large numbers of cells(106-109 cells/g) should be
ıngested for developing the symptoms.
• Diarrhea is usually fallow by low grade fever,
abdominal pain, malaise and nausea
7. b.Enteropathogenic Escherichia coli
• Humans are an important reservoir of
enteropathogenic E. coli (EPEC).Many types of
foods(meat products, fish, milk, milk products,
vegetables, baked products and water canbe
contaminated with EPEC.
• EPEC strains are importantt in infant diarrhea
worldwide and have high mortality rate,
especially in places with poor sanitation.
• High numbers of cells (106-109 cells/g)should be
ingested to develop symptoms