Investigation of serotype distribution and resistance genes profile in group B Streptococcus isolated from pregnant women: a Chinese multicenter cohort study

We surveyed the group B Streptococcus (GBS) strains isolated from four teaching hospitals during 1-year period to investigate the current serotypes and antimicrobial resistance status of these strains. A total of 231 non-duplicate colonizing GBS isolates were collected from pregnant women. Antimicrobial susceptibility of these isolates was tested by the disk diffusion method. Serotype was performed by a multiplex polymerase chain reaction (PCR) method. Analysis of the resistance mechanisms was performed by PCR amplification and DNA sequencing. Seven serotypes (Ia, Ib, II, III, V, VI, and VIII) were identified, and the prevalence ranged from 0.9 to 35.9%. All isolates were susceptible to the penicillin, ceftriaxone, and vancomycin. The resistance of all the isolates to erythromycin, clindamycin, and levofloxacin was 61.5, 51.9, and 35.5%, respectively. The erythromycin resistance was mainly associated with the genes ermB and ermB-mef(A/E) (69.8%). The most predominant phenotype was cMLSB (77.5%). Five gene panels, including gyrA, parC, parE, gyrA-parC, and gyrA-parC-parE, were detected. The most predominant genotype was gyrA-parC-parE triple mutation (69.5%). The S81L in gyrA gene, S79Y mutation in parC gene, and H225Y mutation in parE gene were discovered. The isolates with serotype III, V, and Ia were the most important clone concerning the prevalence and resistance.