长春地区猪链球菌对大环内酯和林克酰胺类耐药的分子机制研究

目的　分析长春地区猪链球菌耐大环内酯类和林克酰胺类的分子机制。方法　采用微量稀释法和双纸片扩散法分别测定相关抗生素的耐药谱和红霉素耐药型 ,并以猪链球菌的染色体DNA为模板 ,PCR扩增ermB基因和mefA/E基因 ,然后将其克隆到pMD18-T载体中 ,用双脱氧链末端终止法测定DNA序列后进行序列分析。结果　 2 2株猪链球菌的临床分离菌株均扩增出ermB基因 ,而未扩增出mefA/E基因 ;对四环素、环丙沙星和大环内酯和克林霉素有高的耐药率和耐药水平 ;红霉素的耐药型以CR型为主。同源性分析显示 ,ermB基因的差异为 36 %～ 10 0 % ,与GenBank中的肺炎链球菌、粪肠球菌等的erm基因有 98%～ 10 0 %的同源性。结论　长春地区猪链球菌对MLSB 的耐药是红霉素甲基化转移酶所介导的 ,以CR型为主的耐药 ,编码该类耐药的是ermB基因 ,并与人源及动物源性的耐药基因可能存在着广泛的交换。

Study on the molecular mechanism of drug-resistance of Streptococcus suis to macrolides in Changchun

To investigate the molecular mechanism of drug-resistance of Streptococcus suis to macrokides,the drug-resistance patterns of the related antibiotics and the erythromycin phenotype were determined by means of micro-dilution assay and double disk diffusion method,and the ermB and mefA/E genes of all the bacterial strains were amplified by PCR with genomic DNA used as templates.It was found that the ermB gene was amplified from 22 strains of the clinical isolates of S.suis,but not for the mefA/E gene,all showing high resistance rates and levels against tetracycline,cipfloxacine,macrolides and lincosamides,with a predominance of CR type resistance of erythromycin Results of sequence analysis showed differences among the S suis strains and the homology analysis revealed a gene difference of 36-100% in ermB gene.Compared with the sequences of Streptococcus pneumoniae and Enterococcus faecalis in GenBank,there was over 98% homology among these organisms.It concludes that the drug-resistance of S.sius isolates to MLS_B in Changchun area is mediated by erythromycin methylation transferase,and the gene encoding for the drug-resistance is ermB gene.It is possible that this gene might be exchanged with the genes of human and animal origins.