Microbiology Coursework: Bacillus Cereus
Microbiology Coursework: Bacillus cereus
After investigation following on outbreak of food poisoning at a pizza restaurant, it was found that all suffers had consumed a portion of side salad from the self-service salad bar alongside their main dish. Subsequently, this was further traced to a rice salad. Environmental Health Officers investigating this outbreak suspected it may have been caused by Bacillus cereus (B. cereus).
The presence of large numbers of B. cereus in a food is indicative of active growth and proliferation of the organism and is consistent with a potential hazard to health. The diagnosis of B. cereus can be confirmed by the isolation of more than 105 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 1. Design a method(s) to enumerate the:
i) Total bacterial count ii) Bacillus cereus count
In the rice salad
This outbreak of food poisoning could be investigated by performing an enumeration (plate count) of the total viable bacteria in the rice salad on a general non-selective agar using either the pour or the spread plate method.
To confirm that the outbreak had been caused by any B. cereus present in the rice salad a selective media agar, such as mannitol egg yolk polymixin agar (MEYP/MYP), should be used. Once B. cereus has been confirmed a further enumeration of the B. cereus should be performed on the MEYP/MYP agar selective media plate to show whether the amount of B. cereus present is within the range known to cause food poisoning 105–107 cells g−1 of food for Diarrhoeal syndrome, or 105–108 cells g−1 of food for Emetic syndrome. (Granum & Lund, 2006)
To perform a total cell count and the confirmation of B.cereus by either the pour or spread plate method the equipment required is as follows:
General non-selective agar
Mannitol egg yolk polymixin agar (MEYP/MYP)
Petri dishes
Glass or
After investigation following on outbreak of food poisoning at a pizza restaurant, it was found that all suffers had consumed a portion of side salad from the self-service salad bar alongside their main dish. Subsequently, this was further traced to a rice salad. Environmental Health Officers investigating this outbreak suspected it may have been caused by Bacillus cereus (B. cereus).
The presence of large numbers of B. cereus in a food is indicative of active growth and proliferation of the organism and is consistent with a potential hazard to health. The diagnosis of B. cereus can be confirmed by the isolation of more than 105 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 1. Design a method(s) to enumerate the:
i) Total bacterial count ii) Bacillus cereus count
In the rice salad
This outbreak of food poisoning could be investigated by performing an enumeration (plate count) of the total viable bacteria in the rice salad on a general non-selective agar using either the pour or the spread plate method.
To confirm that the outbreak had been caused by any B. cereus present in the rice salad a selective media agar, such as mannitol egg yolk polymixin agar (MEYP/MYP), should be used. Once B. cereus has been confirmed a further enumeration of the B. cereus should be performed on the MEYP/MYP agar selective media plate to show whether the amount of B. cereus present is within the range known to cause food poisoning 105–107 cells g−1 of food for Diarrhoeal syndrome, or 105–108 cells g−1 of food for Emetic syndrome. (Granum & Lund, 2006)
To perform a total cell count and the confirmation of B.cereus by either the pour or spread plate method the equipment required is as follows:
General non-selective agar
Mannitol egg yolk polymixin agar (MEYP/MYP)
Petri dishes
Glass or
References: Microbial Growth. (2011). Retrieved March 3, 2012, from The Growth Of Bacterial Cultures: http://classes.midlandstech.com/carterp/Courses/bio225/chap06/Microbial%20Growth%20ss5.htm Donovan, K. O. (1958). A selective medium for Bacillus cereus in milk. J. Appl.Bact.(21), 100-103. Granum, P., & Lund, T. (2006, January 17). Bacillus cereus and its food poisoning toxins. FEMS Microbiology Letters, 157(2), 223-228. doi:10.1111/j.1574-6968.1997.tb12776.x Herriman, R. (2009, September 13). Food-Borne Intoxication - Bacillus Cereus. Retrieved March 6, 2012, from ezinearticles.com: http://ezinearticles.com/?Food-Borne-Intoxication---Bacillus-Cereus&id=2915150 Johnson, K. M. (1984). Bacillus cereus food-borne illness. An update. J Food Prot, 47, 145–153. Merck. (2012). MYP Agar. Retrieved March 01, 2012, from Merck Microbiology Manual 12th Edition: http://www.mibius.de/out/oxbaseshop/html/0/images/wysiwigpro/MYP_Agar_105267_engl.pdf Tallent, S. M., Rhodehamel , E., Harmon, S. M., & Bennett, R. W. (2012, February 02). BAM: Bacillus cereus. Retrieved March 05, 2012, from FDA U.S. Food and Drug Administration: http://www.fda.gov/Food/ScienceResearch/LaboratoryMethods/BacteriologicalAnalyticalManualBAM/ucm070875.htm