Zhao T, Doyle M P, Shere J, Garber L
Center for Food Safety and Quality Enhancement, University of Georgia, Griffin 30223, USA.
Appl Environ Microbiol. 1995 Apr;61(4):1290-3. doi: 10.1128/aem.61.4.1290-1293.1995.
The prevalence of Escherichia coli O157:H7 in dairy herds is poorly understood, even though young dairy animals have been reported to be a host. From February to May 1993, 662 fecal samples from 50 control herds in 14 states, and from June to August 1993, 303 fecal samples from 14 case herds in 11 states were collected for isolation of E. coli O157:H7. Case herds were those in which E. coli O157:H7 was isolated from preweaned calves in a previous U.S. Department of Agriculture study, whereas control herds from which E. coli O157:H7 had not been isolated previously were randomly selected from the same states as case herds. Among the control herds, E. coli O157:H7 was isolated from 6 of 399 calves (1.5%) that were between 24 h old and the age of weaning and from 13 of 263 calves (4.9%) that were between the ages of weaning and 4 months. Eleven of 50 control herds (22%) were positive. Among the case herds, E. coli O157:H7 was isolated from 5 of 171 calves (2.9%) that were between 24 h old and the age of weaning and from 7 of 132 calves (5.3%) that were between the ages of weaning and 4 months. Seven of 14 case herds (50%) were positive. Sixteen of 31 isolates were obtained by direct plating, with populations ranging from 10(3) to 10(5) CFU/g. Fifteen of 31 isolates were isolated by enrichment only. Nineteen of the isolates produced both verocytotoxin 1 (VT-1) and VT-2, whereas 12 produced VT-2 only.
尽管有报道称幼年奶牛是大肠杆菌O157:H7的宿主，但人们对其在奶牛群中的流行情况了解甚少。1993年2月至5月，从14个州的50个对照牛群中采集了662份粪便样本，1993年6月至8月，从11个州的14个病例牛群中采集了303份粪便样本，用于分离大肠杆菌O157:H7。病例牛群是指在美国农业部之前的一项研究中，从断奶前犊牛中分离出大肠杆菌O157:H7的牛群，而对照牛群是指之前未分离出大肠杆菌O157:H7的牛群，它们是从与病例牛群相同的州中随机选取的。在对照牛群中，在399头24小时龄至断奶龄的犊牛中有6头（1.5%）分离出大肠杆菌O157:H7，在263头断奶龄至4月龄的犊牛中有13头（4.9%）分离出该菌。50个对照牛群中有11个（22%）呈阳性。在病例牛群中，在171头24小时龄至断奶龄的犊牛中有5头（2.9%）分离出大肠杆菌O157:H7，在132头断奶龄至4月龄的犊牛中有7头（5.3%）分离出该菌。14个病例牛群中有7个（50%）呈阳性。31株分离菌中有16株是通过直接平板接种获得的，菌量范围为10(3)至10(5) CFU/g。31株分离菌中有15株仅通过增菌培养分离得到。19株分离菌产生了志贺毒素1（VT-1）和VT-2，而12株仅产生VT-2。
