Dominance of clonal complex 10 among the levofloxacin-resistant Streptococcus agalactiae isolated from bacteremic patients in a Korean hospital.

Streptococcus agalactiae has emerged as an important cause of invasive infection in adults. Forty-nine S. agalactiae isolates (41 from adults and 8 from neonates) were collected during a 4-year period (2010-2013) and analyzed by multilocus sequence typing (MLST). Antibiotic susceptibility to erythromycin, clindamycin and levofloxacin was determined and the determinants of resistance (ermA, ermB, ermC, mefA, lnuB) were detected by PCR and mutation in gyrA, gyrB, parC and parE gene was investigated by sequence analysis. They were resolved into 14 sequence types (STs) and belonged to five clonal complexes (CCs). The distribution of CC was significantly different according to the age group; CC1 (18/41) and CC10 (13/41) was the most common among the adult isolates but CC19 (5/8) was predominant among the neonatal isolates. The resistance rate to erythromycin, clindamycin was 18.4% and 24.5%, respectively. Among the 13 strains resistant to erythromycin and/or clindamycin, two isolates harbored ermA and 10 isolates harbored ermB. The levofloxacin resistance rate was very high (32.7%) and was significantly higher in CC10 (71.4%). All the levofloxacin-resistant isolates had identical gyrA substitution (Ser81Leu) but parC substitution was different according to the CCs. The additional mutation in parE (His221Tyr) was found only in CC19. Continuous monitoring of the fluoroquinolone resistance and genotypic distribution among S. agalactiae is needed.