摘要

       大约 20% 的美国肉牛在过渡到饲养场期间接受预防性饲料中金霉素 (CTC) 管理，以减少牛呼吸道疾病 (BRD) 的发病率。为了确定预防措施对选定的抗菌素耐药基因 (ARG) 的影响，将 300 头肉牛放入 10 个围栏（30 头/围栏）。五只“CTC 组”栏在到达饲养场后的第 5 天至第 9 天接受饲料中 CTC（10 mg/lb 体重/天），而五只“对照组”栏没有接受 CTC。在五个样本场合收集粪便拭子和笔表面材料用于宏基因组 DNA 分离：到达饲养场、5 天后处理 (dpt) 和 27、75 和 117 dpt。对于每个样品场合，粪便样品和笔表面材料样品由笔汇集。定量聚合酶链反应用于确定 10 个 ARG 的丰度。由于检测百分比 (%D) 和定量百分比 (%Q) 较低，因此未分析五种 ARG 的丰度：aac(6')-Ie-aph(2'') (%D = 43%, %Q = 4%）、blaCMY-2（%D = 41%、%Q = 0%）、blaCTX-M（%D = 0%、%Q = 0%）、blaKPC-2（%D = 21%、%Q = 16%）和 mecA（%D = 4%，%Q = 0%）。 ARGs aadA1、erm(B)、tet(A)、tet(B)和tet(M)的%D和%Q分别≥98%和≥90%。在粪便或笔表面的任何采样时间，CTC 组和对照组之间的 aadA1、erm(B)、tet(A)、tet(B) 和 tet(M) 抗性基因的丰度没有差异（p > 0.05）材料。尽管在本研究中只检查了 10 种 ARG，但结果表明，肉牛单一 5 天的饲料中 CTC 预防以防止 BRD 对 ARG 丰度的影响可以忽略不计。

       Approximately 20% of U.S. beef cattle receive prophylactic in-feed administration of chlortetracycline (CTC) to reduce bovine respiratory disease (BRD) incidence during the transition into feedlots. To determine the impact of prophylaxis on selected antimicrobial resistance genes (ARGs), 300 beef cattle were placed into 10 pens (30 head/pen). Five “CTC group” pens received in-feed CTC (10 mg/lb of body weight/d) from the fifth to ninth day after feedlot arrival, whereas the five “Control group” pens received no CTC. Fecal swabs and pen surface materials were collected for metagenomic DNA isolation on five sample occasions: arrival at the feedlot, 5 d posttreatment (dpt), and 27, 75, and 117 dpt. For each sample occasion, fecal samples and pen surface material samples were pooled by pen. Quantitative polymerase chain reaction was used to determine the abundances of 10 ARGs. Due to low detection percentages (%D) and quantification percentages (%Q), the abundances of five ARGs were not analyzed: aac(6′)-Ie-aph(2′′) (%D = 43%, %Q = 4%), blaCMY-2 (%D = 41%, %Q = 0%), blaCTX-M (%D = 0%, %Q = 0%), blaKPC-2 (%D = 21%, %Q = 16%), and mecA (%D = 4%, %Q = 0%). The %D and %Q for the ARGs aadA1, erm(B), tet(A), tet(B), and tet(M) were ≥98% and ≥90%, respectively. The abundances of aadA1, erm(B), tet(A), tet(B), and tet(M) resistance genes did not differ (p > 0.05) between the CTC and control groups at any sampling time for feces or pen surface material. Although only 10 ARGs were examined in this study, the results suggest that a single 5-d in-feed CTC prophylaxis of beef cattle to prevent BRD has a negligible impact on the abundances of ARGs.

https://www.liebertpub.com/doi/abs/10.1089/fpd.2018.2475