Bacillus cereus - MegaMicro

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Bacillus cereus

Microbiology > Bacteriology > Gram-positive bacteria > Gram-positive Bacilli > Bacillus
1. Structure
a.Gram positive, non-encapsulated
b. Rod-shaped
c. Motile – flagella
d. β-hemolytic
2. Pathobiology/Virulence Factors:
a. Facultative anaerobe
b. Forms heat resistant, hydrophobic spores
c. Diarrheal
i. Viable cells and secrete endotoxins
ii. Enterotoxins – all three required for maximal enterotoxin activity
1.Hemolysin BL – dermonecrotic  and vascular permeability
a. Primary virulence factor in diarrhea
2. Non-hemolytic enterotoxin
3. Cytotoxin K
d. Emetic
i. Toxin produced in foods when warmed
ii. Cereulid – resistant to heat, pH, proteolysis
3. Epidemiology
a. Ubiquitous in nature – normal soil anaerobe
b. Generally foodborne, usually due to survival of endospores in improperly cooked food
c. Often associated dishes that are cooked and warmed for several hours such as rice
4. Laboratory diagnosis
a. Isolation of > 105 organisms per gram in implicated food
b. Testing usually not done due to self-limiting and relatively harmless nature
5. Disease manifestations
a. Symptoms
i. Emetic – short-incubation
1. Nausea, vomiting, abdominal cramps
2. 1-2 hour incubation, 24 hour duration
ii. Diarrheal – long-incubation
1. Diarrhea, abdominal pain, cramps
2. Incubation period of up to one day in GI, 24 hour duration
iii. Also known to cause skin infections and keratitis
b. Diagnosis
i. Usually diagnosed based on symptoms and possible exposure
c. Differential diagnoses
i. Clostridium perfringens – almost identical presentation to diarrheal
1. Fever is uncommon in B. cereus
d. Therapy
i. Generally resolves after 24 hours – treat symptoms (supportive)
1. Rest and fluids/electrolytes – severe dehydration may require IV fluids
ii. Drug therapy for more severe cases
1. Susceptible to vancomycin, ciprofloxacin, erythromycin, gentamicin, clindamycin, tetracycline
2. Resistant to β-lactams
e. Prevention and control
i. Cook foods thoroughly
ii. Maintain food storage at < 40 °F and > 140 °F
iii. Refrigerate food immediately after cooking

Related concepts

Key Words
1.       Bacillus
2.       Cereus
3.       Gram positive
4.       Rod
5.       Foodborne illness
6.       Food poisoning
7.       Fried rice syndrome
8.       Enterotoxin
9.       Diarrhea

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