Background: Group B Streptococcus (Streptococcus agalactiae, GBS) is a major cause of severe infections in neonates, including bacteremia, pneumonia, and meningitis, and is generally vertically transmitted from a colonized, pregnant woman to her infant. Penicillin is the drug of choice to treat GBS infections, because GBS strains are uniformly susceptible to penicillin. Recently, however, penicillin resistant GBS strains have been reported and the rates of erythromycin and clindamycin resistance have increased. We evaluated the perineal colonization rates and antimicrobial susceptibility of GBS strains isolated from pregnant and non-pregnant women.

Methods: The antibiotic susceptibilities of a total of 180 GBS strains isolated from two university hospitals and one reference laboratory between May 2008 and January 2009 were determined using disk diffusion and broth microdilution methods. The presence of erythromycin resistance genes was confirmed by PCR.

Results: The average colonization rate of pregnant women was 5.5%. The overall colonization rates of pregnant and non-pregnant women ranged between 5.5% and 7.5%. All 180 GBS strains were susceptible to penicillin. Fifty strains (27.8%) were resistant to erythromycin, whereas 78 (41.1%) were resistant to clindamycin. The ermB gene was identified in 40 isolates and 44 isolates had constitutive macrolide- lincosamide-streptogramin B resistance phenotypes.

Conclusion: Our findings indicate an increased GBS colonization rate and an increase in macrolide resistance in GBS strains in recent years, emphasizing the need for further surveillance and continual monitoring of antimicrobial susceptibility. (Korean J Clin Microbiol 2009;12:180-185)