Animal Population Health Institute, Colorado State University, Fort Collins, Colorado, USA.
Foodborne Pathog Dis. 2011 Jan;8(1):87-98. doi: 10.1089/fpd.2010.0632. Epub 2010 Oct 30.
The primary objective was to evaluate differences in antimicrobial resistance among enteric bacteria recovered from feedlot cattle that were being raised without exposure to antimicrobial drugs (AMDs) and those reared using conventional practices.
Forty pens of feedlot cattle (4557 total animals) that were being fed without AMD exposures were selected for enrollment as were 44 pens of cattle (4913 total animals) being fed for production of conventional beef products at the same feedlots. Fecal samples were collected from the floors of pens approximately biweekly through the middle of the feeding period and again prior to slaughter. Samples were cultured to recover nontype-specific Escherichia coli (NTSEC) and Salmonella enterica, and isolates were evaluated for susceptibility to a panel of AMDs.
Cattle enrolled in the study did not differ between groups in entry weight or finish weight, but cattle with restricted AMD and hormone exposures were fed for an average of 50 days longer than conventionally reared cattle (p < 0.001). Resistance among NTSEC isolates was most common to tetracycline, streptomycin, and sulfamethoxazole, and there were slightly higher prevalence of resistance among NTSEC isolates recovered from conventionally reared cattle. Therapeutic AMD exposures did not have a detectable impact on the prevalence of resistance among NTSEC. Although there were detectable temporal trends through the feeding period for resistance to tetracycline, naladixic acid, chloramphenicol, and cephalothin, the direction of trends differed among drugs and these trends were not associated with study groups. S. enterica was recovered rarely (0.73%) but at similar prevalences from cattle with both rearing methods.
These findings suggest that conventional feedlot production methods (including parenteral and in-feed use of AMDs) do not predictably or uniformly increase the prevalence of antimicrobial resistance among fecal NTSEC when compared with rearing methods that restrict exposure to AMDs.
主要目的是评估未接触抗生素（AMD）饲养的育肥牛和常规饲养育肥牛的肠道细菌的抗药性差异。
从同一牛场的 40 个无 AMD 暴露的育肥牛栏（共 4557 头动物）和 44 个常规饲养生产常规牛肉产品的牛栏（共 4913 头动物）中选择粪便样本。大约每两周从栏位地板上收集粪便样本，直到饲养中期，并在屠宰前再次收集。对样本进行培养以回收非特定型大肠杆菌（NTSEC）和肠炎沙门氏菌，并评估分离株对一组 AMD 的敏感性。
研究中纳入的牛在进入体重或结束体重方面没有差异，但受限制的 AMD 和激素暴露的牛的饲养时间比常规饲养的牛平均长 50 天（p<0.001）。NTSEC 分离株的耐药性最常见于四环素、链霉素和磺胺甲恶唑，而从常规饲养的牛中回收的 NTSEC 分离株的耐药性略高。治疗性 AMD 暴露对 NTSEC 的耐药性流行没有明显影响。尽管在饲养期间，四环素、萘啶酸、氯霉素和头孢噻吩的耐药性存在可检测的趋势，但药物之间的趋势方向不同，这些趋势与研究组无关。肠炎沙门氏菌的回收率很低（0.73%），但两种饲养方式的牛的回收率相似。
这些发现表明，与限制 AMD 暴露的饲养方法相比，常规的牛场饲养方法（包括肌肉注射和饲料中使用 AMD）不会可预测或均匀地增加粪便 NTSEC 的抗药性流行率。
