天津地区沙眼衣原体野生株耐药鉴定及机制探索

Antibiotic-resistance identification of the Chlamydia trachomatis wild strains in Tianjin and study on its mechanism

目的:研究天津地区30株沙眼衣原体野生株体外药物敏感性及对四环素的耐药机制。方法:在细胞培养的基础上检测沙眼衣原体野生株对四环素、阿奇霉素及莫西沙星的敏感性,发现耐药菌株后,抽提出耐药菌株的质粒DNA,应用PCR方法对抽提出的DNA进行扩增,并对扩增产物测序。结果:四环素最低抑菌浓度(MIC)≤0.313 mg/L有3株,MIC在0.313～0.625mg/L的有3株,0.625-1.250 mg/L的有8株,1.250-2.500 mg/L的有10株,MIC在2.500-5.000 mg/L的有4株,在5.000-10.000mg/L的有2株;阿奇霉素MIC<0.125 mg/L的为0株,在0.125-0.250 mg/L的有17株,在0.250-0.500 mg/L的有13株。莫西沙星的MIC均集中在0.060-0.120 mg/L之间。用四环素耐药决定因子(tetM)的引物对耐四环素的2株野生株的质粒DNA进行PCR扩增,2株均在约300bp处出现1条明亮的条带;另1株敏感菌株扩增结果均为阴性。测序结果显示扩增产物与淋球菌tetM98.36%同源。结论:天津地区已出现了对四环素耐药的沙眼衣原体野生株,检测的菌株对阿奇霉素和莫西沙星敏感。耐药菌株的质粒DNA包含tetM基因片段,考虑该耐药株的发生机制可能系由质粒介导的。

Objective： To detect the in vitro susceptibilities of Chlamydia trachomatis （Ct） to tetracycline, azithromycine and moxifloxacin and study the possible resistance mechanism. Methods： Thirty wild Ct isolates were cultured in McCoy cells with drugs of a series of concentrations. MIC was detected. The resistance wild strains found were detected with PCR for resistance gene in order to study the possible mechanism of resistance. Results： Two wild strains were resistant to tetracycline （MIC〉5 mg/L） and others were sensitive. All the wild strains detected were sensitive to azithromycine and moxifloxacine with MIC〈0.5 mg/L and MIC〈0.12 mg/L respectively. Two resistance strains were amplified with the primers of tetracycline resistant determinant（tetM）. The amplified results were positive while four sensitive strains all negative. Conclusions： In Tianjin the clinical wild isolates of Ct have already been resistant to tetracycline. The resistant strains are sensitive to azithromyeine and moxifloxacine, TetM gene segments are amplified from the plasmid DNA of the two resistance strains so the mechanism might be that the transposon carried tetM integrated into the plasmid DNA to express resistance. Further study is needed to support this assumption.