Alexander T W, Yanke L J, Topp E, Olson M E, Read R R, Morck D W, McAllister T A
Agriculture and Agri-Food Canada Research Centre, 5403 1st Ave. South, P.O. Box 3000, Lethbridge, Alberta T1J 4B1, Canada.
Appl Environ Microbiol. 2008 Jul;74(14):4405-16. doi: 10.1128/AEM.00489-08. Epub 2008 May 23.
Antibiotic-resistant Escherichia coli in 300 feedlot steers receiving subtherapeutic levels of antibiotics was investigated through the collection of 3,300 fecal samples over a 314-day period. Antibiotics were selected based on the commonality of use in the industry and included chlortetracycline plus sulfamethazine (TET-SUL), chlortetracycline (TET), virginiamycin, monensin, tylosin, or no antibiotic supplementation (control). Steers were initially fed a barley silage-based diet, followed by transition to a barley grain-based diet. Despite not being administered antibiotics prior to arrival at the feedlot, the prevalences of steers shedding TET- and ampicillin (AMP)-resistant E. coli were >40 and <30%, respectively. Inclusion of TET-SUL in the diet increased the prevalence of steers shedding TET- and AMP-resistant E. coli and the percentage of TET- and AMP-resistant E. coli in the total generic E. coli population. Irrespective of treatment, the prevalence of steers shedding TET-resistant E. coli was higher in animals fed grain-based compared to silage-based diets. All steers shed TET-resistant E. coli at least once during the experiment. A total of 7,184 isolates were analyzed for MIC of antibiotics. Across antibiotic treatments, 1,009 (13.9%), 7 (0.1%), and 3,413 (47.1%) E. coli isolates were resistant to AMP, gentamicin, or TET, respectively. In addition, 131 (1.8%) and 143 (2.0%) isolates exhibited potential resistance to extended-spectrum beta-lactamases, as indicated by either ceftazidime or cefpodoxime resistance. No isolates were resistant to ciprofloxacin. The findings of the present study indicated that subtherapeutic administration of tetracycline in combination with sulfamethazine increased the prevalence of tetracycline- and AMP-resistant E. coli in cattle. However, resistance to antibiotics may be related to additional environmental factors such as diet.
通过在314天内收集3300份粪便样本，对300头接受亚治疗水平抗生素的饲养场育肥牛中的耐抗生素大肠杆菌进行了调查。根据该行业使用的普遍性选择抗生素，包括金霉素加磺胺二甲嘧啶（TET-SUL）、金霉素（TET）、维吉尼亚霉素、莫能菌素、泰乐菌素，或不添加抗生素（对照）。育肥牛最初饲喂以大麦青贮为基础的日粮，随后过渡到以大麦谷物为基础的日粮。尽管在到达饲养场之前未使用抗生素，但排出耐TET和氨苄青霉素（AMP）大肠杆菌的育肥牛患病率分别>40%和<30%。日粮中添加TET-SUL增加了排出耐TET和AMP大肠杆菌的育肥牛患病率以及耐TET和AMP大肠杆菌在总大肠埃希菌群体中的百分比。无论治疗如何，与以青贮为基础的日粮相比，饲喂以谷物为基础日粮的动物排出耐TET大肠杆菌的育肥牛患病率更高。在实验期间，所有育肥牛至少有一次排出耐TET大肠杆菌。共分析了7184株分离株的抗生素最低抑菌浓度。在所有抗生素处理中，分别有1009株（13.9%）、7株（0.1%）和3413株（47.1%）大肠杆菌分离株对AMP、庆大霉素或TET耐药。此外，如头孢他啶或头孢泊肟耐药所示，分别有131株（1.8%）和143株（2.0%）分离株对超广谱β-内酰胺酶表现出潜在耐药性。没有分离株对环丙沙星耐药。本研究结果表明，四环素与磺胺二甲嘧啶的亚治疗给药增加了牛中耐四环素和AMP大肠杆菌的患病率。然而，对抗生素的耐药性可能与其他环境因素如日粮有关。
