Lethbridge Research Centre, Agriculture and Agri-Food Canada, Lethbridge T1J 4B1, Alberta.
Appl Environ Microbiol. 2009 Nov;75(22):7125-34. doi: 10.1128/AEM.00944-09. Epub 2009 Oct 2.
Model fecal deposits from cattle fed or not fed antimicrobial growth promoters were examined over 175 days in the field for growth and persistence of total Escherichia coli and numbers and proportions of ampicillin-resistant (Amp(r)) and tetracycline-resistant (Tet(r)) E. coli. In addition, genotypic diversity and the frequency of genetic determinants encoded by Amp(r) and Tet(r) E. coli were investigated. Cattle were fed diets containing chlortetracycline (44 ppm; A44 treatment group), chlortetracycline plus sulfamethazine (both at 44 ppm; AS700 treatment group), or no antibiotics (control). Fecal deposits were sampled 12 times over 175 days. Numbers of Tet(r) E. coli in A44 and AS700 deposits were higher (P < 0.001) than those of controls and represented up to 35.6% and 20.2% of total E. coli, respectively. A time-by-treatment interaction (P < 0.001) was observed for the numbers of Tet(r) and Amp(r) E. coli. Except for Amp(r) E. coli in control deposits, all E. coli numbers increased (P < 0.001) in deposits up to day 56. Even after 175 days, high Tet(r) E. coli numbers were detected in A44 and AS700 deposits [5.9 log(10) CFU (g dry matter)(-1) and 5.4 log(10) CFU (g dry matter)(-1), respectively]. E. coli genotypes, as determined by pulsed-field gel electrophoresis, were diverse and were influenced by the antimicrobial growth promoter and the sampling time. Of the determinants screened, bla(TEM1), tetA, tetB, tetC, sul1, and sul2 were frequently detected. Occurrence of determinants was influenced by the feeding of antimicrobials. Fecal deposits remain a source of resistant E. coli even after a considerable period of environmental exposure.
研究人员在野外对 175 天内投喂或未投喂抗菌生长促进剂的牛的粪便样本进行了研究，以检测总大肠杆菌的生长和持续时间，以及氨苄青霉素抗性（Amp(r)）和四环素抗性（Tet(r)）大肠杆菌的数量和比例。此外，还研究了 Amp(r)和 Tet(r)大肠杆菌的遗传多样性和编码遗传决定因素的频率。牛饲料中添加了金霉素（44ppm；A44 处理组）、金霉素加磺胺嘧啶（均为 44ppm；AS700 处理组）或无抗生素（对照组）。在 175 天内采集了 12 次粪便样本。A44 和 AS700 粪便中 Tet(r)大肠杆菌的数量更高（P<0.001），分别占总大肠杆菌的 35.6%和 20.2%。数量的时间和处理之间存在交互作用（P<0.001） Tet(r)和 Amp(r)大肠杆菌。除了对照组粪便中的 Amp(r)大肠杆菌外，所有大肠杆菌数量在 56 天内均增加（P<0.001）。即使在 175 天后，A44 和 AS700 粪便中仍检测到高数量的 Tet(r)大肠杆菌[5.9 log(10) CFU（g 干物质）（-1）和 5.4 log(10) CFU（g 干物质）（-1）]。通过脉冲场凝胶电泳确定的大肠杆菌基因型多种多样，并受到抗菌生长促进剂和采样时间的影响。在所筛选的决定因素中，bla(TEM1)、tetA、tetB、tetC、sul1 和 sul2 频繁检出。决定因素的出现受到抗生素的影响。粪便沉积物即使在相当长的环境暴露后，仍然是耐药大肠杆菌的来源。
