肺炎链球菌对大环内酯类抗生素耐药机制研究

目的观察耐大环内酯类肺炎链球菌的耐药表型和基因型。方法用琼脂二倍稀释法测定耐大环内酯类肺炎链球菌对11种抗生素的最低抑菌浓度,耐药表型由红霉素和克林霉素双纸片法初步分型,通过PCR扩增耐药基因ermB和mefA进行基因分型,并测定ermB和mefA基因序列。结果　所有23株肺炎链球菌对大环内酯和克林霉素高度耐药,均表现为内在型耐药,没有发现诱导型耐药和M型耐药。ermB基因在23株肺炎链球菌中均检测到,其中5株同时检测到mefA基因,没有发现仅单一mefA基因阳性的菌株,基因型与耐药表型完全一致。所测ermB和mefA基因序列与基因库收录序列高度一致。 结论ermB基因介导的靶位改变可能是重庆地区肺炎链球菌对大环内酯类抗生素的主要耐药机制。

Study of macrolide resistant mechanism phenotypes and genotypes in Streptococcus pneumoniae

Objective To investigate the prevalence of macrolides resistantphenotypes and genotypes of S. pneumoniae in Chongqing of China. MethodsAntibiotic susceptibility was determined by two-fold agar dilution test accordingto National Committee for Clinical Laboratory Standards methods. Resistantphenotypes were classified using a double disc test with erythromycin andclindamycin discs. ermB and mefA genes were amplified by PCR and sequenced.Results All 23 S.pneumoniae were highly resistant to all macrolides andclindamycin. Twenty three strains were constitutive resistant without a singleinducible resistant strain, and showed not the M-resistant phenotype. Theconstitutive resistant phenotype were genetically confirmed by the presence ofthe ermB gene in all 23 strains, both ermB and mefA genes were found in only 5 strainsat the same time. DNA sequencing demonstrated that the sequences of ermB andmefA genes were identical to the sequences deposited in Genbank under accessionNo. of AJ243540 and AF274302. Conclusion The target modification mediated byermB methylase is the predominant mechanism of macrolide resistance in S.pneumoniae isolated in Chongqing.