A Comparative Analysis of Molecular Epidemiology and Antibiotic Resistance in Group B Streptococcus Isolated From Invasive and Noninvasive Adult Cases in Daejeon, South Korea

Background: This study aims to determine the molecular features and antimicrobial resistance of Streptococcus agalactiae (Group B streptococcus, GBS) causing invasive and noninvasive infections in Korean adults. Methods: Sequence type (ST), capsular serotype, pilus island typing, and antimicrobial susceptibility were analyzed for GBS isolates obtained at a hospital laboratory that processed the primary clinical specimens collected from Korean adults between 2021 and 2024. Results: Among the 90 isolates, Serotype VIII (34.4%) was the most common, followed by V (17.8%), Ia (12.2%), VI (11.1%), II (10.0%), and Ib (6.7%). Every isolate contained at least one PI gene, of which PI2a (37.8%) was the most frequently observed combination. The combination of PI1 and PI2b was present in 34.4% of isolates, followed by PI1 and PI2a (24.4%) and PI2b alone (3.3%). Among the 18 STs identified, the capsular serotype VIII/ST2–clonal complex 1 (CC1) was dominant (34.4%), followed by V or VI/ST1 (12.2%). All isolates were susceptible to both ampicillin and vancomycin, while antibiotic resistances were observed for erythromycin (27.8%), levofloxacin (13.3%), clindamycin (25.6%), and tetracycline (47.8%), respectively. Conclusions: These data are key elements to help design prevention and treatment strategies for GBS infection in Korean adults.