Bacillus cereus - MegaMicro

a.Gram positive, non-encapsulated

b. Rod-shaped

c. Motile – flagella

d. β-hemolytic

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

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

a. Isolation of > 105 organisms per gram in implicated food

b. Testing usually not done due to self-limiting and relatively harmless nature

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