Lin S, Schraft H, Odumeru J A, Griffiths M W
Department of Food Science, University of Guelph, Ontario, Canada.
Int J Food Microbiol. 1998 Sep 8;43(3):159-71. doi: 10.1016/s0168-1605(98)00105-6.
In order to determine the sources of Bacillus cereus in pasteurized milk, a total of 232 milk samples from various sampling points along milk processing lines and 122 environmental swabs were collected in two dairy plants between March and September, 1996. The incidence of B. cereus vegetative cells in raw milk from the plants was low (< or = 10%). However, the incidence and the average counts of B. cereus spores in the raw milk were very high and similar to those of B. cereus vegetative cells in pasteurized milk or final products after enrichment (> 80% and 1.1 x 10(5) cfu ml(-1), respectively). The incidence and average count of both vegetative cells and spores of B. cereus in environmental swabs was low. Using the microbial identification system (MIDI), a library of B. cereus fatty acid profiles comprising 229 B. cereus isolates from milk samples and environmental swabs was constructed using a critical Euclidian distance of 6.0 units as the cut-off value. Using this library, the relationship between 546 B. cereus isolates from the different sampling points along the milk processing lines and the environmental swabs was determined. Most B. cereus isolates obtained from the pasteurized milk and final products belonged to the same sub-groups as the B. cereus strains germinated from spores in raw milk. Furthermore, specific sub-groups were found in pasteurized milk, different dairy plants and at different sampling times. The results suggested that B. cereus spores in raw milk were the major source of B. cereus in pasteurized milk and that post-pasteurization contamination along the milk processing lines was possibly a minor source of B. cereus in pasteurized milk.
为确定巴氏杀菌乳中蜡样芽孢杆菌的来源，1996年3月至9月期间，在两家乳制品厂共采集了232份沿牛奶加工生产线不同采样点的牛奶样本以及122份环境拭子。这些工厂原料乳中蜡样芽孢杆菌营养细胞的发生率较低（≤10%）。然而，原料乳中蜡样芽孢杆菌芽孢的发生率和平均计数非常高，与富集后巴氏杀菌乳或最终产品中蜡样芽孢杆菌营养细胞的发生率和平均计数相似（分别>80%和1.1×10⁵ cfu/ml）。环境拭子中蜡样芽孢杆菌营养细胞和芽孢的发生率及平均计数均较低。使用微生物鉴定系统（MIDI），以6.0单位的临界欧氏距离作为截断值，构建了一个包含来自牛奶样本和环境拭子的229株蜡样芽孢杆菌脂肪酸谱库。利用该谱库，确定了沿牛奶加工生产线不同采样点的546株蜡样芽孢杆菌分离株与环境拭子之间的关系。从巴氏杀菌乳和最终产品中获得的大多数蜡样芽孢杆菌分离株与原料乳中芽孢萌发的蜡样芽孢杆菌菌株属于同一亚组。此外，在巴氏杀菌乳、不同乳制品厂以及不同采样时间发现了特定的亚组。结果表明，原料乳中的蜡样芽孢杆菌芽孢是巴氏杀菌乳中蜡样芽孢杆菌的主要来源，而牛奶加工生产线巴氏杀菌后的污染可能是巴氏杀菌乳中蜡样芽孢杆菌的次要来源。
