B. cereus is responsible for a minority of foodborne illnesses (2–5%), causing severe
nausea,
vomiting, and
diarrhea.
Bacillus foodborne illnesses occur when
B. cereus spores or bacteria contaminate food and are allowed to survive cooking, and then given sufficient time to
germinate, multiply, and produce toxins in the food. Normal cooking methods such as boiling, stewing, or steaming at reliably kill
Bacillus cereus vegetative cells, but do not reliably destroy heat-resistant
spores. The risk is increased when cooked food is then slowly cooled or left within the temperature "
danger zone", which is between to , allowing spores to germinate.
FDA's Food Code 2017 recommends that cooked food not meant for immediate consumption is cooled rapidly and
refrigerated promptly at temperatures below , or is kept hot above . Refrigeration does not destroy bacteria but inhibits or slows their growth. Germination and growth generally occur between 10 °C and 50 °C, and Bacillus cytotoxicus strains have been shown to grow at temperatures up to . Bacterial growth results in production of
enterotoxins, one of which is highly resistant to heat and acids (
pH levels between 2 and 11); ingestion leads to two types of illness: diarrheal and emetic (vomiting) syndrome. The enterotoxins produced by
B. cereus have beta-hemolytic activity. • The 'emetic' form commonly results from rice which is cooked at a time and temperature insufficient to kill any spores present, then improperly refrigerated. The remaining spores can produce a
toxin,
cereulide, which is not inactivated by later reheating. This form leads to nausea and vomiting 1–5 hours after consumption. Distinguishing from other short-term bacterial foodborne intoxications, such as by
Staphylococcus aureus, can be difficult. The diarrhetic syndromes observed in patients are thought to stem from the three toxins:
hemolysin BL (Hbl), nonhemolytic
enterotoxin (Nhe), and
cytotoxin K (CytK). The
nhe/
hbl/
cytK genes are located on the chromosome of the bacteria. Transcription of these genes is controlled by
PlcR. These genes occur in the taxonomically related
B. thuringiensis and
B. anthracis, as well. These enterotoxins are all produced in the small intestine of the host, thus thwarting digestion by host endogenous enzymes. The Hbl and Nhe toxins are pore-forming toxins closely related to
ClyA of
E. coli. The proteins exhibit a conformation known as a "
beta-barrel" that can insert into cellular membranes due to a
hydrophobic exterior, thus creating pores with
hydrophilic interiors. The effect is loss of cellular
membrane potential and eventually cell death. Previously, it was thought that the timing of the toxin production was responsible for the two different courses of disease, but it has since been found that the emetic syndrome is caused by the toxin
cereulide, which is found only in emetic strains and is not part of the "standard toolbox" of
B. cereus. Cereulide is a cyclic polypeptide containing three repeats of four amino acids: -oxy-—-—-oxy-—- (similar to
valinomycin produced by
Streptomyces griseus) produced by
nonribosomal peptide synthesis. Cereulide is believed to bind to 5-hydroxytryptamine 3 (5-HT3)
serotonin receptors, activating them and leading to increased
afferent vagus nerve stimulation. It was shown independently by two research groups to be encoded on multiple
plasmids: pCERE01 or pBCE4810. Plasmid pBCE4810 shares homology with the
B. anthracis virulence plasmid pXO1, which encodes the
anthrax toxin. Periodontal isolates of
B. cereus also possess distinct pXO1-like plasmids. Like most of cyclic peptides containing nonproteogenic amino acids, cereulide is resistant to heat, proteolysis, and acid conditions.
B. cereus is also known to cause difficult-to-eradicate chronic skin infections, though less aggressive than
necrotizing fasciitis.
B. cereus can also cause
keratitis. While often associated with gastrointestinal illness,
B. cereus is also associated with illnesses such as fulminant bacterial infection, central nervous system involvement, respiratory tract infection, and endophthalmitis. Endophthalmitis is the most common form of extra-gastrointestinal pathogenesis, which is an infection of the eye that may cause permanent vision loss. Infections typically cause a corneal ring abscess, followed by other symptoms such as pain, proptosis, and retinal hemorrhage. While different from
B. anthracis, B. cereus contains some toxin genes originally found in
B. anthracis that are attributed to anthrax-like respiratory tract infections. A case study was published in 2019 of a
catheter-related bloodstream infection of
B. cereus in a 91-year-old male previously being treated with
hemodialysis via PermCath for end-stage
renal disease. He presented with chills,
tachypnea, and high-grade fever, his
white blood cell count and
high-sensitivity C-reactive protein (CRP) were significantly elevated, and
CT imaging revealed a thoracic
aortic aneurysm. He was successfully treated for the infection with intravenous
vancomycin, oral
fluoroquinolones, and PermCath removal. Another case study of
B. cereus infection was published in 2021 of a 30-year-old woman with lupus who was diagnosed with infective endocarditis after receiving a catheter. The blood samples were positive for B. cereus and the patient was subsequently treated with vancomycin. PCR was also used to verify toxins that the isolate produces.
Diagnosis In case of
foodborne illness, the diagnosis of
B. cereus can be confirmed by the isolation of more than 100,000
B. cereus organisms per gram from epidemiologically implicated food, but such testing is often not done because the illness is relatively harmless and usually self-limiting.
Prognosis Most emetic patients recover within 6 to 24 hours, In 2014, 23 newborns in the UK receiving
total parenteral nutrition contaminated with
B. cereus developed
sepsis, with three of the infants later dying as a result of infection.
Prevention While
B. cereus vegetative cells are killed during normal cooking, spores are more resistant. Viable spores in food can become vegetative cells in the intestines and produce a range of diarrheal enterotoxins, so elimination of spores is desirable. In wet heat (poaching, simmering, boiling, braising, stewing, pot roasting, steaming), spores require more than 5 minutes at at the coldest spot to be destroyed. In dry heat (grilling, broiling, baking, roasting, searing, sautéing), for 1 hour kills all spores on the exposed surface. This process of eliminating spores is very important, as spores of
B. cereus are particularly resistant, even after pasteurization or exposure to gamma rays. A study of an isolate of
Bacillus cereus that was isolated from the stomach of a sheep was shown to be able to break down β-
cypermethrin (β-CY) which has been known to be an antimicrobial agent. This strain, known as GW-01, can break down β-CY at a significant rate when the bacterial cells are in high concentrations relative to the antimicrobial agent. It has also been noted that the ability to break down β-CY is inducible. However, as the concentration of β-CY increases, the rate of β-CY degradation decreases. This suggests that the agent also functions as a toxin against the GW-01 strain. This is significant as it shows that in the right concentrations, β-CY can be used as an antimicrobial agent against
Bacillus cereus. ==Diseases in aquatic animals==