title: Effect of low-dose irradiation on growth of and toxin production by Staphylococcus aureus and Bacillus cereus in roast beef and gravy.
abstract: The effect of irradiation (2 kGy) on growth of and toxin production by Staphylococcus aureus and Bacillus cereus in roast beef and gravy during storage at abuse temperatures (15 and 22 degrees C) was assessed by inoculation studies. Irradiation resulted in a 3-4 log10 reduction in numbers of both pathogens. Whenever B. cereus and S. aureus numbers reached 10(6) and 10(7) cfu/g, respectively, during storage their toxins were detectable. As the time taken to attain these levels was longer in irradiated than in unirradiated samples, toxin production by both pathogens was delayed by irradiation. When samples initially containing low levels (10(2)/g) of S. aureus were irradiated no toxin was produced during subsequent storage at 15 or 22 degrees C. Diarrhoeal toxin produced by B. cereus was detected after 2 days at 22 degrees C, but not at 15 degrees C, in samples containing 10(2) cells/g prior to irradiation. When higher numbers (10(6)/g) of either pathogen were present prior to irradiation, toxins were produced by both pathogens at 22 degrees C, but not at 15 degrees C. Microbial competition had an effect on the growth of B. cereus and S. aureus after irradiation when a low initial inoculum was applied. However, when a higher inoculum was used the pathogens outnumbered their competitors and competition effects were less important. It was concluded that low-dose irradiation would improve the microbiological safety of roast beef and gravy.
authors: Department of Food Microbiology, Queen's University of Belfast, Northern Ireland, UK.
authors: I R
authors: IR
authors: Grant
authors: C R
authors: CR
authors: Nixon
authors: M F
authors: MF
authors: Patterson
mesh_terms: D000818:Animals; D001409:Bacillus cereus / Q000254:growth & development / Q000378:metabolism / Q000528:radiation effects*; D001427:Bacterial Toxins / Q000096:biosynthesis; D002417:Cattle; D005514:Food Irradiation; D005516:Food Microbiology; D005517:Foodborne Diseases / Q000517:prevention & control; D006801:Humans; D008460:Meat / Q000382:microbiology* / Q000528:radiation effects*; D011829:Radiation Dosage; D012449:Safety; D013211:Staphylococcus aureus / Q000254:growth & development / Q000378:metabolism / Q000528:radiation effects*
chemical_list: D001427:Bacterial Toxins