Genomic epidemiology of Group B Streptococcus colonization among pregnant women in Japan, 2021-2023.

Authors

Chizu Nishi, Hirofumi Ohtaki, Masaki Karino, Hiromi Uekita, Ayumi Sano, Tetsuya Kobayashi, Susumu Kaino, Yoshiki Sakamoto, Satoshi Nakano

Published in

PloS one. Volume 21. Issue 7. Pages e0354799. Epub Jul 30, 2026.

Abstract

Group B Streptococcus (GBS) colonization in pregnant women is a major risk factor for neonatal diseases; however, molecular epidemiological studies on GBS in Japan remain limited. We characterized 219 GBS isolates recovered from vaginal screening cultures at a general hospital in Osaka Prefecture, Japan between 2021 and 2023. Capsular type, clonal complex/sequence type (CC/ST), virulence factors (pilus islands, Alp family, Srr1/Srr2, and HvgA), and antimicrobial resistance determinants were analyzed using whole-genome sequencing. The predominant lineages were CC19 (27.9%), CC23 (21.9%), and CC1 (21.0%), whereas the hypervirulent CC17 lineage accounted for only 5.5% of isolates. Capsular type Ia, III, and V comprised >60% of the isolates. PI-1/PI-2a (58.0%) was the predominant pilus profile, and rib (35.2%) was the most frequent Alp family gene. The hypervirulence-associated markers hvgA and srr2 were confined to capsular types III/CC17 and IV/CC452. All isolates were susceptible to β-lactams and vancomycin, whereas resistance to macrolides, clindamycin, and levofloxacin was observed at varying frequencies. These findings provide a pre-vaccine molecular baseline for maternal GBS carriage in Japan and highlight srr2-positive CC452 as a potential emerging lineage of concern.

PMID:
42531347
Bibliographic data and abstract were imported from PubMed on 31 Jul 2026.

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