Bacillus cereus is a Gram-positive, rod-shaped, motile, spore-forming bacterium that causes food poisoning, primarily through its diarrheal and emetic toxins found in various foods, notably rice. It is widespread in nature and can survive in diverse conditions, including high temperatures and acidic environments. The bacterium can be isolated using selective media and has potential probiotic applications that may improve food safety in animal products.

1. BACILLUS CEREUS
SPECIES: B. CEREUS
CLASS: BACILLI
GENUS: BACILLUS
FAMILY: BACILLACEAE
ORDER: BACILLALES
PHYLUM: FIRMICUTES
DOMAIN: BACTERIA

2. The word Bacillus means “Small rod” cereus
means “Wax-like”
It is derived from Lathin language.
The name itself reflects the morphology of
Bacillus cereus

3. 1.Gram positive
2.Rod shape
3.Motile
4.Spore forming
5.Facultative anaerobe
Characteristics of Bacillus cereus

4. Size
Length : 3-5 μm
Width : 1-1.2 μm
Optimum condition for growth
Temperature : 30-37⁰c
pH: 6-7
Maximum toxin production occur at 20-
25⁰c

5. Bacillus cereus contains two enzymes
ALKC
ALKD
Involved in DNA repair

6. For survival :
Temperature :
Spores more resistant to dry heat than moist heat.
It also more resistant in oily foods.
Cooking at or below 100⁰C may allow spore
survival.
pH:
Vegetative cells decline generally rapidly in
stomach acid. Some may survive depending on
food and level of stomach acidity.
Spores are resistant to gastric acidity between
pH 1-5.2.

7. Sources of B.cereus
It is wide spread in nature and frequently
isolated from soil and growing plants, but it
also adapted for growth in the intestinal tract
of insects and mammals
It is becoming one of the important causes of
food poisoning in the industrialized world.

8. Bacillus cereus produce two
type of toxins:
1.Diarrheal toxin: 38-57k Da
2.Emetic toxin: 10k Da
Transmission is predominantly food borne for both.

9. Diarrheal type
1.Found in food such as vegetables, meat, poultry,
grains.
2.It causes fever, diarrhoea.
3.Incubation period 8-16 hrs.
4.Cause sick at night or early in the morning.
5.Toxin secreted in our intestine.
6.Toxin-Heat labile.

10. Emetic type
1.Found specifically in rice.
2.Commonly called fried rice syndrome.
3.It cause vomiting, abdominal pain.
4.Very short incubation period 1-5 hrs.
5.Toxin-Heat labile.

11. Selective media
MYPA - Mannitol yolk polymyxin B
agar
MYPA- contains peptone, mannitol, sodium
chloride, phenol red, agar.
B.cereus produce dry pink red colonies.

12. PEMBA – Polymyxin pyruvate egg yolk
mannitol bromothymol blue agar
PEMPA- contain peptone, mannitol, sodium
pyruvate, disodium phosphate, sodium chloride,
potassium dihydrogen phosphate, magnesium
sulphate, bromothymol blue, agar.
B.cereus produce forest green opaque gel forms.

13. Bacaria agar
Chromogenic selective and differential agar that
promote the growth and identification of B.cereus.
Inhibit the growth of backround flora.
B.cereus produce pink orange colour on bacaria
agar.

14. Bacillus cereus
Susceptible to Clindamycin, Erythromycin,
Vancomycin.
Resistance to
Penicillin, Trimethoprim.

15. Bacillus cereus as probiotic
Certain strain producing small amount of toxin at 37⁰C.It have been
approved probiotic.
Bacillus cereus used as a probiotic food additive to reduce
salmonella in the animal intestines & cecum.
This improve animal growth as well as food safety for human who
eat them.

16. Preservatives
Sorbic acid
Benzoate
Sorbate
Polyphosphates
EDTA
Disinfectants
Chlorine
Sodium hypochloride are effective against B.cereus but
not spores.

17. Sporocidal
Formaldehyde
Iodine
Acid
Alkalis
peroxy acids
Ozone
Phenolics,Alcohols,Organic acids,Esters,Mercurial have
little sporocidal effects.

18. ISOLATION
25g sample into 225 ml buffered peptone water.
Prepare serial dilution (9ml dilution blank + 1ml of sample)
Prepare MYP Agar plates
Take 10-1 to 10-3 dilution
From each dilution 0.1ml spread plated on MYP Agar plates
Allow the inoculum to dry

19. Incubate 30˚ C for 24 hrs
After incubation, examine the plates
Bacillus cereus produce typical colonies which are usually surrounded by a precipitate caused by
Lacithinase activity
If reaction on the MYP agar plates are not clear incubate plates for an additional 24 hrs
Pick 5 or more presumptive positive colonies from MYP agar plates and transfer to Nutrient agar slant
Bacillus cereus conformed by Biochemical reactions

20. BIOCHEMICAL ANALYSIS
1. Catalase: positive
2. Oxidase: negative
3. Indole: negative
4. Methyl red: positive
5. Vogues proskauer: positive
6.Simmon citrate: positive
7. Glucose: fermentative, production of acid
8. Sucrose: fermentative, production of acid
9. Lactose: no fermentation
10. Starch hydrolysis: positive
11. Nitrate reduction: positive
12. Gelatin hydrolysis: positive

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