Molecular characterization of adult-colonizing Streptococcus agalactiae from an area-based surveillance study in...

One hundred and forty-eight colonizing isolates from adult Romanian women were conventionally serotyped and screened for antibiotic resistance. Capsular type assignment by multiplex polymerase chain reaction (PCR) was performed for nonserotypeable isolates. Tetracycline and macrolide resistance genes (tetM, tetO, tetL, ermA, ermB, and mefA) including tetM gene association with conjugative elements of the Tn916 family were searched. Molecular typing included PCR screening for major surface protein antigen genes (bac, bca, alp1, alp2/3, alp4, and rib), mobile genetic elements (GBSi1 and IS1548), and rapid detection of hypervirulent clone ST-17. Genetic diversity was assessed by pulsed field gel electrophoresis (PFGE) analysis of SmaI macrorestriction patterns. Among the colonizing isolates studied, serotypes V and III predominated and high rates of tetracycline and macrolide resistance were observed. The tetM gene occurred in 140 tetracycline-resistant isolates and was associated with the int-Tn916 gene in 94 of them. Most of the isolates displayed a constitutive MLS(B) phenotype (38/46 isolates) and harbored the ermB gene. rib, alp2/3, and alp1 were the most common surface protein genes detected. Either IS1548 or GBSi1 intron were detected in almost half of the isolates and nine serotype III isolates belonged to clone ST-17. PFGE analysis of SmaI macrorestriction patterns, obtained from 118 isolates, revealed an apparent genetic diversity.