Food Microbiology Laboratory, Department of Food Science, University of Massachusetts, Amherst, Massachusetts 01003, USA.
J Food Prot. 2009 Nov;72(11):2386-9. doi: 10.4315/0362-028x-72.11.2386.
Bacillus cereus is a gram-positive, spore-forming, facultative anaerobe that is responsible for two types of gastrointestinal diseases: emesis and diarrhea. A significant difference in the D(95 degrees C)-values of spores of the emetic and the diarrheal types was initially determined. A mixture of B. cereus spores of the diarrheal type was inoculated into cooked rice. At inoculation levels of 2.5 x 10(2) spores per g of rice, cell numbers of 6.64 log were detected after 22 h at 20 degrees C and 6.81 log after 34 h at 17 degrees C, whereas at 12 degrees C the counts did not go above 4.0 log even after 48 h. When added to raw rice before cooking at inoculum levels of 10(3)/g, the number of viable spores decreased by 2 log, and a <1-log increase in cell numbers occurred after holding at 20 degrees C for 24 h. In contrast, the emetic spores survived and increased approximately 20-fold. Nonhemolytic enterotoxin was not detected in cooked rice at cell numbers of 8.0 log. Results here provide evidence that the absence of foodborne illness caused by the B. cereus diarrheal biotype with rice as the vehicle is due to the inability of their spores to survive and grow following standard heat processing procedures.
蜡样芽胞杆菌是一种革兰氏阳性、产芽孢、兼性厌氧细菌，可引起两种类型的胃肠道疾病：呕吐型和腹泻型。最初确定了呕吐型和腹泻型芽孢的 D（95°C）值存在显著差异。将腹泻型蜡样芽胞杆菌的孢子混合物接种到煮熟的米饭中。在接种水平为每克米饭 2.5 x 10(2)个孢子的情况下，在 20°C下 22 小时后检测到 6.64 log 的细胞数，在 17°C下 34 小时后检测到 6.81 log，而在 12°C下即使经过 48 小时，计数也不会超过 4.0 log。当在 10(3)/g 的接种水平添加到生米中进行烹饪前，活菌数减少了 2 个对数，在 20°C下保持 24 小时后，细胞数仅增加了 1 个对数。相比之下，呕吐型孢子存活下来并增加了约 20 倍。在细胞数为 8.0 log 的煮熟米饭中未检测到非溶血性肠毒素。结果表明，由于其孢子在标准热加工过程后无法存活和生长，因此以米饭为载体的蜡样芽胞杆菌腹泻型不会引起食源性疾病。
