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Bacillus cereus

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Bacillus cereus
B. cereus colonies on sheep blood agar plate.
Scientific classification
Kingdom:
Bacteria
Phylum:
Firmicutes
Class:
Bacilli
Order:
Bacillales
Family:
Bacillaceae
Genus:
Bacillus
Species:
cereus
Binomial name
Bacillus cereus
Frankland & Frankland 1887

Bacillus cereus is an endemic, soil-dwelling, Gram-positive, rod-shaped, beta hemolytic bacterium. Some strains are harmful to humans and cause foodborne illness, while other strains can be beneficial as probiotics for animals.[1] B. cereus bacteria are facultative anaerobes, and like other members of the genus Bacillus can produce protective endospores.

Symbiosis

B. cereus competes with other microorganisms such as Salmonella and Campylobacter in the gut, so its presence reduces the numbers of those microorganisms. In food animals such as chickens,[2] rabbits[3] and pigs,[4] some harmless strains of B. cereus are used as a probiotic feed additive to reduce Salmonella in the intestines and cecum. This improves the animals' growth as well as food safety for humans who eat their meat.

Pathogenesis

B. cereus is responsible for a minority of foodborne illnesses (2–5%), causing severe nausea, vomiting and diarrhea.[5] Bacillus foodborne illnesses occur due to survival of the bacterial endospores when food is improperly cooked.[6] This problem is compounded when food is then improperly refrigerated, allowing the endospores to germinate.[7] Bacterial growth results in production of enterotoxins, one of which is highly resistant to heat and to pH between 2 and 11;[8] ingestion leads to two types of illness, diarrheal and emetic (vomiting) syndrome.[9]

  • The diarrheal type is associated with a wide-range of foods, has an 8- to 16.5-hour incubation time and is associated with diarrhea and gastrointestinal pain. Also known as the long-incubation form of B. cereus food poisoning, it might be difficult to differentiate from poisoning caused by Clostridium perfringens.[8]
  • The emetic form is commonly caused by rice that is not cooked for a time and temperature sufficient to kill any spores present, then improperly refrigerated. It can produce a toxin, cereulide, which is not inactivated by later reheating. This form leads to nausea and vomiting 1–5 hours after consumption. It can be difficult to distinguish from other short-term bacterial foodborne pathogens such as Staphylococcus aureus.[8]

The diarrhetic syndromes observed in patients is thought to stem from the three toxins Hemolysin BL Hbl, Nonhemolytic Enterotoxin Nhe and Cytotoxin K CytK.[10] The nhe/hbl/cytK genes are located on the chromosome of the bacteria. Transcription of these genes is controlled by PlcR. These genes occur as well in the toxonomically related B. thuringensis and B. anthracis. These enterotoxins are all produced in the small intestine of the host, thus thwarting the issue of 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 "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. CytK is a pore-forming protein more related to other hemolysins.

It was previously thought that the timing of the toxin production might be responsible for the two different courses of disease, but in fact the emetic syndrome is caused by a toxin called cereulide that is found only in emetic strains and is not part of the "standard toolbox" of B. cereus. Cereulide contains 3 repeats of 4 amino acids (similar to Valinomycin produced by Streptomyces griseus) produced by nonribosomal peptide synthesis (NRPS). Cereulide is believed to activate 5-HT3 (serotonin) receptors leading to increased afferent vagus nerve stimulation.[11] It was shown independently by two research groups to be encoded on multiple plasmids: pCERE01[12] or pBCE4810.[13] Plasmid pBCE4810 shares homology with the Bacillus anthracis virulence plasmid pXO1, which encodes the anthrax toxin. Periodontal isolates of B. cereus also possess distinct pXO1-like plasmids.

B. cereus is also known to cause chronic skin infections that are difficult to eradicate though less aggressive than necrotizing fasciitis. B. cereus can also cause keratitis.[14] It recommended as pathogenic microflora in pharmaceutical oral products in Brazilian Phamacopaeia.[citation needed]

References

  1. ^ Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill. ISBN 0-8385-8529-9. {{cite book}}: |author= has generic name (help)CS1 maint: multiple names: authors list (link)
  2. ^ Vilà, B (2009). "Reduction of Salmonella enterica var. Enteritidis colonization and invasion by Bacillus cereus var. toyoi inclusion in poultry feeds". Poultry Science. 88 (55). HighWire Press: 975–9. doi:10.3382/ps.2008-00483. PMID 19359685. Retrieved 14 May 2009. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  3. ^ Bories, Georges (9 December 2008). "Safety and efficacy of the product Toyocerin (Bacillus cereus var. toyoi) as feed additive for rabbit breeding does - Scientific Opinion of the Panel on Additives and Products or Substances used in Animal Feed" (PDF). European Food Safety Authority. EFSA-Q-2008-287. Retrieved 14 May 2009. {{cite journal}}: Cite journal requires |journal= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help); line feed character in |coauthors= at position 69 (help)
  4. ^ Bories, Georges (EFSA-Q-2006-037). "Opinion of the Scientific Panel on Additives and Products or Substances used in Animal Feed on the safety and efficacy of the product Toyocerin (Bacillus cereus var. Toyoi) as a feed additive for sows from service to weaning, in accordance with Regulation (EC) No 1831/2003" (PDF). European Food Safety Authority. Retrieved 14 May 2009. {{cite journal}}: Check date values in: |date= (help); Cite journal requires |journal= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  5. ^ Kotiranta A, Lounatmaa K, Haapasalo M (2000). "Epidemiology and pathogenesis of Bacillus cereus infections". Microbes Infect. 2 (2): 189–98. doi:10.1016/S1286-4579(00)00269-0. PMID 10742691.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  6. ^ Turnbull PCB (1996). Bacillus. In: Baron's Medical Microbiology (Barron S et al., eds.) (4th ed.). Univ of Texas Medical Branch. (via NCBI Bookshelf) ISBN 0-9631172-1-1.
  7. ^ McKillip JL (2000). "Prevalence and expression of enterotoxins in Bacillus cereus and other Bacillus spp., a literature review". Antonie Van Leeuwenhoek. 77 (4): 393–9. doi:10.1023/A:1002706906154. PMID 10959569.
  8. ^ a b c "Bacillus cereus". Todar's Online Textbook of Bacteriology. Retrieved 19 September 2009.
  9. ^ Ehling-Schulz M, Fricker M, Scherer S (2004). "Bacillus cereus, the causative agent of an emetic type of food-borne illness". Mol Nutr Food Res. 48 (7): 479–87. doi:10.1002/mnfr.200400055. PMID 15538709.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  10. ^ Enterotoxigenic Profiles of Food-Poisoning and Food-Borne Bacillus cereus Strains Marie-Hélène Guinebretière,* Véronique Broussolle, and Christophe Nguyen-TheInstitut National de la Recherche Agronomique, UMR A408 Sécurité et Qualité des Produits d'Origine Végétale, INRA, Domaine Saint-Paul, Site Agroparc, F-84914 Avignon Cedex 9, France. PMCID: PMC120679
  11. ^ Agata N, Ohta M, Mori M, Isobe M (1995). "A novel dodecadepsipeptide, cereulide, is an emetic toxin of Bacillus cereus". FEMS Microbiol Lett. 129 (1): 17–20. doi:10.1016/0378-1097(95)00119-P. PMID 7781985.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  12. ^ Hoton FM, Andrup L, Swiecicka I, Mahillon J (2005). "The cereulide genetic determinants of emetic Bacillus cereus are plasmid-borne". Microbiology. 151 (7): 2121–4. doi:10.1099/mic.0.28069-0. PMID 16000702.{{cite journal}}: CS1 maint: multiple names: authors list (link) CS1 maint: unflagged free DOI (link)
  13. ^ Ehling-Schulz M, Fricker M, Grallert H, Rieck P, Wagner M, Scherer S (2006). "Cereulide synthetase gene cluster from emetic Bacillus cereus: structure and location on a mega virulence plasmid related to Bacillus anthracis toxin plasmid pXO1". BMC Microbiol. 6 (20): 20. doi:10.1186/1471-2180-6-20. PMC 1459170. PMID 16512902.{{cite journal}}: CS1 maint: multiple names: authors list (link) CS1 maint: unflagged free DOI (link)
  14. ^ Pinna A, Sechi LA, Zanetti S; et al. (2001). "Bacillus cereus keratitis associated with contact lens wear". Ophthalmology. 108 (10): 1830–4. doi:10.1016/S0161-6420(01)00723-0. PMID 11581057. {{cite journal}}: Explicit use of et al. in: |author= (help); Unknown parameter |month= ignored (help)CS1 maint: multiple names: authors list (link)
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