中文摘要：

作者拟探讨禽源支原体对替米考星耐药的分子机制。体外诱导得到鸡毒支原体（R株、PG31株和S6株）、鸡滑液支原体、衣阿华支原体的替米考星耐药株;PCR扩增原始敏感株和诱导耐药株的23S rRNA基因V域,测序分析耐药相关碱基突变情况。结果鸡毒支原体R株、PG31株、S6株、鸡滑液支原体、衣阿华支原体分别通过9代、8代、6代、14代、9代诱导获得替米考星耐药（≥128μg.mL-1）株;3种禽源支原体替米考星诱导耐药株均对大环内酯类药物表现交叉耐药,23SrRNA基因发生A2503T突变的诱导耐药株对截短侧耳素类、氯霉素类药物的敏感性明显降低。诱导获得的替米考星耐药鸡毒支原体R株发生了A2058G和A2503T突变,PG31株发生了A2058G和A2059G突变,S6株发生了A2058G和A2503T突变;而诱导获得的替米考星耐药鸡滑液支原体发生了G2162A突变,衣阿华支原体发生了A2059C突变。本研究表明鸡毒支原体和衣阿华支原体在体外较易经替米考星诱导产生耐药性,而鸡滑液支原体相对较难。菌株23SrRNA基因V域2 058、2 059、2 503位点的碱基突变与替米考星耐药表型有密切关系。

英文摘要：

This experiment was conducted to study the mechanisms of resistance to tilmicosin in three avian Mycoplasma species.Resistant mutants were selected by serial transfers of M.gallisepticum（strains R,S6 and PG31）,M.synoviae and M.iowae in Frey＇s broth medium containing stepwise increasing concentrations of tilmicosin.For the parental strains and tilmicosin-resistant mutants obtained in this study,the genes encoding domain Ⅴof 23S rRNA were amplified by PCR and sequenced.Tilmicosin-resistance（≥128 μg·mL-1）strains of M.gallisepticum strains R,S6,PG31,M.synoviae and M.iowae were obtained through 9,8,6,14 and 9 passages,respectively.All the resistant mutants selected by tilmicosin were cross-resistant to macrolides,and the mutants harboring the A2503T mutation showed less-susceptible to pleuromutilin and phenicol antibiotics.The tilmicosin-resistant mutant derived from M.gallisepticum R harbored A2058G and A2503T mutations.The mutant derived from M.gallisepticum PG31 harbored A2058G and A2059G mutations.The mutant derived from M.gallisepticum S6 harbored A2058G and A2503T mutations.The mutant derived from M.synoviae possessed a G2162A mutation.The mutant derived from M.iowae possessed an A2059C mutation.Tilmicosin-resistance developed readily in M.gallisepticum and M.iowae,whereas tilmicosin-resistance developed only after greater numbers of passages in M.synoviae.Mutations at positions 2 058,2 059 and 2 503 of 23S rRNA gene are associated with resistance to tilmicosin in the three avian Mycoplasma species.