Diversity and distribution of commensal fecal Escherichia coli bacteria in beef cattle administered selected subtherapeutic antimicrobials in a feedlot setting
Diversity and distribution of commensal fecal Escherichia coli bacteria in beef cattle administered selected subtherapeutic antimicrobials in a feedlot setting
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DOI：
10.1128/aem.00704-08
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发表时间：
2008-10-01
影响因子：
4.4
通讯作者：
McAllister, Tim
中科院分区：
文献类型：
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作者：
Sharma, Ranjana;Munns, Krysty;McAllister, Tim
筛选从粪便样本中分离的大肠杆菌菌株，以检查表型和基因型特征的变化，包括抗菌药物敏感性、克隆类型和耐药决定簇的携带。这项为期197天的研究旨在研究金霉素单独给药（T）或与磺胺二甲嘧啶（TS）联合给药对饲养场牛耐药性发展、确定菌株类型传播和耐药性决定因素流行的影响。在既往未暴露于抗菌剂的牛中检测到固有的四环素耐药性。未发现抗菌药物给药对于维持固有的氨苄青霉素耐药和四环素耐药（泰特（r））E.而Tetr E.在接受两种处理的动物中观察到大肠杆菌脱落。在第0天，检测到高四环素（26.7%）、低磺胺甲恶唑-四环素（19.2%）和其他几种耐药性，到育肥期（第197天），仅限于给药和未给药牛的氨苄青霉素-四环素（47.5%）、四环素（31.7%）和氨苄青霉素-四环素-磺胺甲恶唑（20.8%）。在决定因素中，（bla）（TEM 1）、（泰特）（A）和sul 2在第0天和第197天普遍存在。此外，E.从第0天开始，大肠杆菌显示出不同的细菌谱图和菌株类型，无论处理如何，到完成阶段，细菌谱图和菌株类型被限制为最多三种。一些遗传上相同的菌株表现出不同的表型，并具有不同的决定因素，表明移动的遗传因素有助于抗性传播。氨苄青霉素和四环素耐药基因的连锁遗传增加以及第197天特定菌株的流行支持了这一点。由于动物间的菌株传播，队列中的动物在结束阶段脱落的基因型越来越相似。因此，表征群体特异性菌株的固有耐药性和繁殖对于确定牛的抗菌素耐药性至关重要。
Escherichia coli strains isolated from fecal samples were screened to examine changes in phenotypic and genotypic characteristics including antimicrobial susceptibility, clonal type, and carriage of resistance determinants. The goal of this 197-day study was to investigate the influence of administration of chlortetracycline alone (T) or in combination with sulfamethazine (TS)on the development of resistance, dissemination of defined strain types, and prevalence of resistance determinants in feedlot cattle. Inherent tetracycline resistance was detected in cattle with no prior antimicrobial exposure. Antimicrobial administration was not found to be essential for the maintenance of inherently ampicillin-resistant and tetracycline-resistant (Tet(r)) E. coli in control animals; however, higher Tetr E. coli shedding was observed in animals subjected to the two treatments. At day 0, high tetracycline (26.7%), lower sulfamethoxazole-tetracycline (19.2%), and several other resistances were detected, which by the finishing phase (day 197) were restricted to ampicillin-tetracycline (47.5%), tetracycline (31.7%), and ampicillin-tetracycline-sulfamethoxazole (20.8%) from both treated and untreated cattle. Among the determinants, (bla)(TEM1), (tet)(A), and sul2 were prevalent at days 0 and 197. Further, E. coli from day 0 showed diverse antibiogram profiles and strain types, which by the finishing phase were limited to up to three, irrespective of the treatment. Some genetically identical strains expressed different phenotypes and harbored diverse determinants, indicating that mobile genetic elements contribute to resistance dissemination. This was supported by an increased linked inheritance of ampicillin and tetracycline resistance genes and prevalence of specific strains at day 197. Animals in the cohort shed increasingly similar genotypes by the finishing phase due to animal-to-animal strain transmission. Thus, characterizing inherent resistance and propagation of cohort-specific strains is crucial for determining antimicrobial resistance in cattle.