Significant shifts in the distribution of vaccine capsular polysaccharide types and rates of antimicrobial resistance of perinatal group B streptococci within the last decade in St. Petersburg, Russia

Evaluation of circulating group B streptococcus (GBS) strains is important to assess the potential effects of GBS prevention strategies in a certain region. This study aimed at estimating the distributions of capsular polysaccharide (CPS) types and pilus profiles, and the rates of antimicrobial resistance among GBS strains isolated from colonized pregnant women and newborns in 2010–2011 and 2017–2018 in St. Petersburg, Russia. A total of 261 GBS isolates have been investigated. Antibiotic susceptibility testing was performed using the disc-diffusion method. CPS types and pilus profiles were determined by using PCR. Over the 9-year period, the resistance of GBS to both erythromycin and clindamycin has significantly increased, exceeding 30% in 2017–2018. The most prevalent CPS types were Ia, III, and V. Significant shifts were observed in the frequency of CPS types III (decreased) and V (increased), which resulted in a significant reduction (from 77 to 63%) in the potential coverage by a trivalent vaccine (including serotypes Ia, Ib, and III), whereas that of a pentavalent vaccine (including serotypes Ia, Ib, II, III, and V) remained largely unchanged (approximately 95%). The most common pilus profiles were PI-1/2a, PI-2a, and PI-1a/2b, and pilus genotype distribution has not changed with time. High and steadily growing resistance of perinatal GBS strains to clindamycin requires restricting its use to penicillin-allergic women at high risk for anaphylaxis and testing the GBS strains for their susceptibility to this antibiotic. A pentavalent CPS-based vaccine covers the vast majority of perinatal GBS strains in Russia.