Dodd Charles C, Sanderson Michael W, Sargeant Jan M, Nagaraja T G, Oberst Richard D, Smith Robert A, Griffin D Dee
Department of Clinical Sciences, Kansas State University, Manhattan, Kansas 66506, USA.
Appl Environ Microbiol. 2003 Sep;69(9):5243-7. doi: 10.1128/AEM.69.9.5243-5247.2003.
Comparisons of enrichment methods (with or without antibiotics and with or without a preenrichment step) using gram-negative (GN) broth or tryptic soy broth (TSB) were conducted with feeds inoculated with Escherichia coli O157:H7. TSB was more sensitive than GN broth, and TSB with a preenrichment step followed by TSB with antibiotics was more sensitive than plain TSB enrichment, in detecting E. coli O157 in inoculated feeds. Feed samples were collected from feed bunks from 54 feedlots to determine the prevalence of E. coli O157 in cattle feeds. TSB preenrichment followed by TSB with antibiotics and the standard GN broth enrichment were used for each feed sample. All samples underwent immunomagnetic separation and were plated onto sorbitol MacConkey agar with cefixime and potassium tellurite. Identification of E. coli O157 was based on indole production, positive latex agglutination for O157 antigen, API 20E test strip results, PCR for the eaeA gene, and the presence of at least one Shiga toxin. E. coli O157 was detected in 52 of 504 feed samples (10.3%) by using GN broth enrichment and in 46 of 504 feed samples (9.1%) by using TSB followed by TSB supplemented with cefixime and vancomycin. E. coli O157 was detected in 75 of 504 feed bunk samples (14.9%) by one or both methods. There was no correlation between E. coli O157 prevalence and generic coliform counts in feeds. The prevalence of E. coli O157 in cattle feed warrants further studies to increase our knowledge of the on-farm ecology of E. coli O157 in order to develop strategies to prevent food-borne disease in humans.
采用接种了大肠杆菌O157:H7的饲料，对使用革兰氏阴性（GN）肉汤或胰蛋白胨大豆肉汤（TSB）的富集方法（有无抗生素以及有无预富集步骤）进行了比较。在检测接种饲料中的大肠杆菌O157时，TSB比GN肉汤更敏感，先进行预富集步骤再使用含抗生素的TSB进行富集比单纯的TSB富集更敏感。从54个饲养场的饲料槽中采集饲料样本，以确定牛饲料中大肠杆菌O157的流行情况。每个饲料样本均采用先进行TSB预富集再使用含抗生素的TSB以及标准的GN肉汤富集方法。所有样本均经过免疫磁珠分离，并接种到含头孢克肟和亚碲酸钾的山梨醇麦康凯琼脂平板上。基于吲哚产生、O157抗原乳胶凝集阳性、API 20E测试条结果、eaeA基因的聚合酶链反应（PCR）以及至少一种志贺毒素的存在来鉴定大肠杆菌O157。使用GN肉汤富集法在504个饲料样本中的52个（10.3%）检测到大肠杆菌O157，使用先进行TSB富集再使用含头孢克肟和万古霉素的TSB富集法在504个饲料样本中的46个（9.1%）检测到大肠杆菌O157。通过一种或两种方法在504个饲料槽样本中的75个（14.9%）检测到大肠杆菌O157。饲料中大肠杆菌O157的流行情况与总大肠菌群数之间没有相关性。牛饲料中大肠杆菌O157的流行情况值得进一步研究，以增进我们对农场中大肠杆菌O157生态的了解，从而制定预防人类食源性疾病的策略。
