为探讨无乳链球菌对四环素类的敏感性及其与耐药基因、多位点序列分型(multilocus sequence typing，MLST)之间的关系，本研究收集2014—2017年深圳市南山区人民医院分离自患者的136株无乳链球菌临床分离株，采用琼脂平板稀释法分析四环素类最低抑菌浓度(minimum inhibitory concentration，MIC)。采用聚合酶链反应检测菌株四环素类耐药基因(tetM、tetK、tetO)，MLST测定ST型别，并分析四环素类敏感性与其耐药基因及ST型别之间的关系。结果显示，无乳链球菌对四环素类的耐药率为46.32%，耐四环素类菌株主要携带tetM基因，主要为ST17型和ST19型，且ST17型菌株对四环素类的耐药率显著高于ST19型(P<0.05)。结果提示，无乳链球菌的主要四环素类耐药基因为tetM，ST17型、ST19型是主要流行型别，且ST17型菌株对四环素类的敏感性低于ST19型。

The present paper aims to investigate the antimicrobial activity of tetracycline against clinical Streptococcus agalactiae (S. agalactiae) isolates. A total of 136 S. agalactiae isolates were collected retrospectively in Nanshan People’s Hospital between 2014 and 2017. The minimum inhibitory concentrations (MICs) of tetracycline were determined by agar dilution. Polymerase chain reaction (PCR) was used to detect Tet-specific resistance factors and housekeeping genes. The strains were typed by multilocus sequence typing (MLST). The results showed that the resistance rate of S. agalactiae isolates to tetracycline was 46.32% (63/136), and the tetracycline-resistant strains mainly carried tetM. The dominant ST types were ST17 and ST19 strains. The antimicrobial activity of tetracycline against ST17 strains was significantly higher than ST19 strains. It is concluded that the tetracycline resistance in S. agalactiae isolates is associated with tetM gene and the dominant strains are ST17 strains and ST19 strains.