Clinical significance of serotype V among infants with invasive group B streptococcal infections in South Korea

•The serotypes and antibiotic resistance among infants with invasive group B Streptococcus (GBS) disease were analyzed.•Serotypes III (44.6%) and V (28.6%) were the most common, followed by Ia (14.3%).•A large proportion (28.6%) of invasive GBS disease among infants was due to serotype V.•A majority of the serotype V cases showed a high level of resistance to erythromycin and clindamycin.

SummaryBackgroundGroup B Streptococcus (GBS) strains are classified by the polysaccharide capsule, which is an important virulence factor and stimulator of antibody-associated immunity. As GBS infections in neonates may be life-threatening, GBS screening and intrapartum antibiotic prophylaxis have been implemented for prevention. In Korea, there are few reports on the GBS serotype distribution and antibiotic resistance patterns because GBS screening and intrapartum prophylaxis are not done routinely.MethodsThe serotype distribution and antibiotic resistance of GBS in infants in Korea with invasive bacterial infections were examined for the 19-year period 1995–2013. Isolates obtained previously from hospitals located in three different regions were analyzed for capsular serotype by PCR and sequencing and for antimicrobial susceptibility.ResultsAmong 56 isolates serotyped, the most common serotypes were III (44.6%) and V (28.6%), followed by Ia (14.3%), Ib (10.7%), and VI (1.8%). No penicillin-resistant strains were detected, however 51.8% of the strains had resistance to erythromycin and 55.4% showed clindamycin resistance. Resistance was highest (93.8%) to both erythromycin and clindamycin for serotype V; all 15 isolates resistant to erythromycin were cMLSB phenotype and had a high level of resistance to both erythromycin and clindamycin with MIC levels >256 μg/ml, and all but one were positive for ermB.ConclusionIn this study in Korea, serotype V was identified in a relatively large proportion of GBS isolates and this serotype showed a high level of resistance to erythromycin and clindamycin in a statistically significant majority. Continuous monitoring of changes in clinical disease and molecular characteristics is important for the treatment and prevention of invasive GBS disease in infants.