Agriculture and Agri-Food Canada Research Centre, Lethbridge, Alberta T1J 4B1, Canada.
BMC Microbiol. 2011 Jan 24;11(1):19. doi: 10.1186/1471-2180-11-19.
Environmental transmission of antimicrobial-resistant bacteria and resistance gene determinants originating from livestock is affected by their persistence in agricultural-related matrices. This study investigated the effects of administering subtherapeutic concentrations of antimicrobials to beef cattle on the abundance and persistence of resistance genes within the microbial community of fecal deposits. Cattle (three pens per treatment, 10 steers per pen) were administered chlortetracycline, chlortetracycline plus sulfamethazine, tylosin, or no antimicrobials (control). Model fecal deposits (n = 3) were prepared by mixing fresh feces from each pen into a single composite sample. Real-time PCR was used to measure concentrations of tet, sul and erm resistance genes in DNA extracted from composites over 175 days of environmental exposure in the field. The microbial communities were analyzed by quantification and denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S-rRNA.
The concentrations of 16S-rRNA in feces were similar across treatments and increased by day 56, declining thereafter. DGGE profiles of 16S-rRNA differed amongst treatments and with time, illustrating temporal shifts in microbial communities. All measured resistance gene determinants were quantifiable in feces after 175 days. Antimicrobial treatment differentially affected the abundance of certain resistance genes but generally not their persistence. In the first 56 days, concentrations of tet(B), tet(C), sul1, sul2, erm(A) tended to increase, and decline thereafter, whereas tet(M) and tet(W) gradually declined over 175 days. At day 7, the concentration of erm(X) was greatest in feces from cattle fed tylosin, compared to all other treatments.
The abundance of genes coding for antimicrobial resistance in bovine feces can be affected by inclusion of antibiotics in the feed. Resistance genes can persist in feces from cattle beyond 175 days with concentrations of some genes increasing with time. Management practices that accelerate DNA degradation such as frequent land application or composting of manure may reduce the extent to which bovine feces serves as a reservoir of antimicrobial resistance.
环境中抗微生物药物耐药菌和耐药基因决定因子的传播源自于牲畜，其在农业相关基质中的持久性会影响其传播。本研究旨在探究对肉牛施用低于治疗剂量的抗生素对粪便微生物群落中耐药基因丰度和持久性的影响。每处理组设 3 个围栏（每个围栏 10 头牛），分别施用金霉素、金霉素+磺胺甲恶唑、泰乐菌素或不施用抗生素（对照）。通过将每个围栏的新鲜粪便混合到单个复合样本中，制备模型粪便沉积物（n = 3）。通过实时 PCR 测量在野外环境暴露 175 天期间，从复合材料中提取的 DNA 中 tet、sul 和 erm 耐药基因的浓度。通过定量和聚合酶链反应扩增的 16S-rRNA 的变性梯度凝胶电泳（DGGE）分析微生物群落。
粪便中 16S-rRNA 的浓度在处理间相似，并在第 56 天增加，此后下降。16S-rRNA 的 DGGE 图谱在处理间和随时间变化，说明微生物群落随时间发生了变化。在 175 天后，所有测量的耐药基因决定因子在粪便中均可定量。抗生素处理对某些耐药基因的丰度有不同的影响，但通常不会影响其持久性。在最初的 56 天内，tet（B）、tet（C）、sul1、sul2 和 erm（A）的浓度呈上升趋势，此后下降，而 tet（M）和 tet（W）则在 175 天内逐渐下降。在第 7 天，与其他所有处理相比，泰乐菌素组牛粪便中 erm（X）的浓度最高。
牛粪便中编码抗微生物药物耐药性的基因丰度可能受到饲料中抗生素的影响。在 175 天以上的时间里，粪便中仍可检测到某些基因的耐药基因，且其浓度随时间增加。促进 DNA 降解的管理措施（如频繁的土地施用或堆肥）可能会降低牛粪便作为抗微生物药物耐药性储存库的程度。
