通过对肉牛饲喂低于治疗水平的不同种类抗生素,研究其对肉牛废弃粪便微生物群落中四环素耐药基因数量与持久性的影响.试验肉牛被分成不同抗生素处理组,即氯四环素组、氯四环素和磺胺甲嘧啶组及对照组.将每个围栏中所有动物的新鲜粪便混匀为一份混合样品作为模式样品(每个处理组3份),分别露天放置,在第7、14、28、42、56、70、84、98、112、126和175天时采样并提取DNA,利用Real-time PCR方法测定四环素耐药基因tet(B),tet( C),tet(L),tet(M),tet(W)及16S rRNA的浓度.结果显示,16S rRNA的浓度在不同处理间相似,在56 d内均有增加的趋势(P＜0.05)；总体上看,四环素组的耐药基因初始浓度较高(P＜0.05)；所有处理组的tet(B)和tet(C)浓度到56 d时均增长了1～2个对数级,到175 d时又降低到初始水平,而tet(M)与tet(W)的浓度与其他耐药基因相比较高.因此,四环素耐药基因可以在废弃粪便中持续存在超过175 d,而某些基因的最初数量可能会导致错估其后的变化,其浓度的暂时改变并不能归因于微生物群落数量的变化.%This study was investigated the effects of administering beef cattle antimicrobials at subtherapeutic concentrations on the abundance and persistence of tetracycline resistance genes within the whole microbial community of fecal waste . Cattlrnwere administered chlortetracyclinei chlortetracycline plus sulfamethazine and no antimicrobials. Model fecal deposits (n-3) were prepared by mixing fresh feces from pens into a single composite sample. Real-time PCR was used to measure concentrations of tetracycline resistance genes tet(B) , tet(C) , tet(L) , tet(M) , tet(W) and 16S rRNA in DNA extracted from composite feces after 7, 14, 28, 42, 56, 70, 84, 98, 112, 126 and 175 days in the field. The concentrations of 16S rRNA in feces were similar across treatments and increased by day 56. Generally, initial concentrations of tetracycline resistance genes were greater (P<0. 05) in fecal pats from animals fed chlortetracycline. For all fecal treatments, tet(B) and tet(C) increased 1 to 2 log units by 56 d, and then decreased to the initial 7 d levels by 175 d. The concentrations of tet(M) and tet(W) were greater than other tetracycline resistance determinants. Therefore, tetracycline resistance genes could persist in fecal waste from cattle beyond 175 days and the initial load of some genes might underestimate concentrations at later time points. Temporal changes in the concentrations of resistance genes were likely due to shifts in microbial populations.
展开▼
