Shere J A, Bartlett K J, Kaspar C W
Department of Food Microbiology and Toxicology, University of Wisconsin, Madison 53706, USA.
Appl Environ Microbiol. 1998 Apr;64(4):1390-9. doi: 10.1128/AEM.64.4.1390-1399.1998.
A 14-month longitudinal study was conducted on four dairy farms (C, H, R, and X) in Wisconsin to ascertain the source(s) and dissemination of Escherichia coli O157:H7. A cohort of 15 heifer calves from each farm were sampled weekly by digital rectal retrieval from birth to a minimum of 7 months of age (range, 7 to 13 months). Over the 14 months of the study, the cohort heifers and other randomly selected cattle from farms C and H tested negative. Farm R had two separate periods of E. coli O157:H7 shedding lasting 4 months (November 1995 to February 1996) and 1 month (July to August 1996), while farm X had at least one positive cohort animal for a 5-month period (May to October 1996). Heifers shed O157:H7 strains in feces for 1 to 16 weeks at levels ranging from 2.0 x 10(2) to 8.7 x 10(4) CFU per g. E. coli O157:H7 was also isolated from other noncohort cattle, feed, flies, a pigeon, and water associated with the cohort heifers on farms R and/or X. When present in animal drinking water, E. coli O157:H7 disseminated through the cohort cattle and other cattle that used the water source. E. coli O157:H7 was found in water at < 1 to 23 CFU/ml. Genomic subtyping by pulsed-field gel electrophoresis demonstrated that a single O157:H7 strain comprised a majority of the isolates from cohort and noncohort cattle, water, and other positive samples (i.e., from feed, flies, and a pigeon, etc.) on a farm. The isolates from farm R displayed two predominant XbaI restriction endonuclease digestion profiles (REDP), REDP 3 and REDP 7, during the first and second periods of shedding, respectively. Six additional REDP that were > or = 89% similar to REDP 3 or REDP 7 were identified among the farm R isolates. Additionally, the REDP of an O157:H7 isolate from a heifer on farm R in 1994 was indistinguishable from REDP 3. Farm X had one O157:H7 strain that predominated (96% of positive samples had strains with REDP 9), and the REDP of an isolate from a heifer in 1994 was indistinguishable from REDP 9. These results suggest that E. coli O157:H7 is disseminated from a common source on farms and that strains can persist in a herd for a 2-year period.
在威斯康星州的四个奶牛场（C、H、R和X）进行了一项为期14个月的纵向研究，以确定大肠杆菌O157:H7的来源和传播情况。从每个农场选取15头小母牛犊，从出生到至少7月龄（范围为7至13个月）每周通过直肠指检进行采样。在研究的14个月中，C场和H场的同组小母牛以及其他随机选取的牛检测均为阴性。R场有两个独立的大肠杆菌O157:H7排菌期，分别持续4个月（1995年11月至1996年2月）和1个月（1996年7月至8月），而X场有至少一头同组动物在5个月期间（1996年5月至10月）检测为阳性。小母牛在粪便中排出O157:H7菌株的时间为1至16周，每克粪便中的菌量范围为2.0×10²至8.7×10⁴CFU。在R场和/或X场，还从其他非同组牛、饲料、苍蝇、一只鸽子以及与同组小母牛相关的水中分离出了大肠杆菌O157:H7。当存在于动物饮用水中时，大肠杆菌O157:H7会通过同组牛和使用该水源的其他牛进行传播。在水中检测到的大肠杆菌O157:H7含量为每毫升<1至23CFU。通过脉冲场凝胶电泳进行的基因组亚型分析表明，单个O157:H7菌株构成了一个农场中同组和非同组牛、水以及其他阳性样本（即来自饲料、苍蝇和鸽子等）中大多数分离株。R场的分离株在第一个和第二个排菌期分别显示出两种主要的XbaI限制性内切酶消化图谱（REDP），即REDP 3和REDP 7。在R场的分离株中还鉴定出另外六种与REDP 3或REDP 7相似度≥89%的REDP。此外，1994年从R场一头小母牛分离出的O157:H7菌株的REDP与REDP 3无法区分。X场有一个占主导地位的O157:H7菌株（96%的阳性样本具有REDP 9的菌株），1994年从一头小母牛分离出的菌株的REDP与REDP 9无法区分。这些结果表明，大肠杆菌O157:H7在农场中从一个共同来源传播，并且菌株可以在牛群中持续存在两年。
