Department of Population Medicine, Ontario Veterinary College, University of Guelph, Guelph, Canada.
Foodborne Pathog Dis. 2011 Feb;8(2):239-48. doi: 10.1089/fpd.2010.0666. Epub 2010 Oct 30.
The objectives of this study were to compare the performance of different diagnostic protocols (rectoanal mucosal swabs and immunomagnetic separation [RAMS-IMS], fecal samples and IMS [fecal-IMS], and direct plating) to determine the prevalence of Escherichia coli O157:H7 and to evaluate the pattern of E. coli O157:H7 shedding and super-shedding (defined as having a direct plating count equal to or >10(4) colony forming units of E. coli O157:H7 per gram of feces) in a longitudinal study of naturally infected feedlot steers. RAMS and fecal grab samples were obtained at 14-day intervals from 168 Angus-cross beef steers over a period of 22 weeks. Fecal samples were assessed by direct plating and IMS, whereas RAMS were tested only by enrichment followed by IMS to recover E. coli O157:H7. The period prevalence for shedding was high (62%) among feedlot steers and super-shedding was higher (23%) than anticipated. Although direct plating was the least sensitive method to detect E. coli O157:H7-positive samples, over 20% of high bacterial load samples were not detected by RAMS-IMS and/or fecal-IMS. The sensitivity of RAMS-IMS, fecal-IMS, and direct plating protocols was estimated using simple and multilevel mixed-effects logistic regression models, in which the dependent variable was the dichotomous results of each test and gold standard (i.e., parallel interpretation of the three protocols)-positive individuals were included as an independent variable along with other factors such as dietary supplements, time of sampling, and being exposed to a super-shedding pen-mate. The associations between these factors and the sensitivity of the diagnostic protocols were not statistically significant. In conclusion, differences in the reported impact of diet and probiotics on the shedding of E. coli O157:H7 in previous studies using RAMS-IMS or fecal-IMS were unlikely due to their impact on test performance.
本研究的目的是比较不同诊断方案（直肠-肛门黏膜拭子和免疫磁分离[RAMS-IMS]、粪便样本和 IMS[粪便-IMS]以及直接平板培养）的性能，以确定大肠杆菌 O157:H7 的流行率，并评估自然感染牛群中大肠杆菌 O157:H7 的脱落和超脱落（定义为直接平板培养计数等于或大于每克粪便中 10(4)个大肠杆菌 O157:H7 形成单位）的模式。168 头安格斯杂交肉牛在 22 周的时间内每隔 14 天采集一次 RAMS 和粪便抓取样本。通过直接平板培养和 IMS 评估粪便样本，而仅通过富集后 IMS 检测 RAMS 以回收大肠杆菌 O157:H7。牛群中的脱落期流行率很高（62%），超脱落率（23%）高于预期。尽管直接平板培养是检测大肠杆菌 O157:H7 阳性样本最不敏感的方法，但超过 20%的高细菌负荷样本未被 RAMS-IMS 和/或粪便-IMS 检测到。使用简单和多级混合效应逻辑回归模型估计了 RAMS-IMS、粪便-IMS 和直接平板培养方案的敏感性，其中因变量是每个测试和金标准（即三种方案的平行解释）的二分结果阳性个体作为一个独立变量，同时还包括其他因素，如膳食补充剂、采样时间以及暴露于超脱落同舍牛。这些因素与诊断方案敏感性之间的关联没有统计学意义。总之，使用 RAMS-IMS 或粪便-IMS 报道的饮食和益生菌对大肠杆菌 O157:H7 脱落的影响差异不大，这不可能是由于它们对测试性能的影响。
