We investigated the molecular epidemiology of Streptococcus agalactiae (Group B Streptococcus, GBS) from carriage in a cohort of pregnant mothers and their respective newborns in a
Teaching Hospital in Sri Lanka. GBS vaginal carriage was assessed on pregnant mothers at predelivery (n = 250), post-delivery (n = 130), and from peri-rectal swabs of neonates (n = 159) in a
prospective study. All colonizing, non-duplicate GBS isolates (n = 60) were analyzed for antimicrobial
susceptibilities, capsular serotyping, and whole-genome sequencing (WGS). The percentage of GBS
carriage in mothers in the pre-delivery and post-delivery cohorts were 11.2% (n = 28) and 19.2%
(n = 25), respectively, and 4.4% (n = 7) in neonates. GBS isolates predominantly belonged to serotype
VI (17/60, 28.3%). The isolates spanned across 12 sequence types (STs), with ST1 (24/60, 40%) being
the most predominant ST. Concomitant resistance to erythromycin, tetracyclines, and gentamicin
was observed in eight strains (13.3%). WGS revealed the presence of antimicrobial resistance genes
including ermA (5/60), mefA (1/60), msrD (1/60), and tetLMO (2/60, 28/60, and 1/60, respectively)
among 60 strains. The study provides insight into the diversity of vaccine targets of GBS since
serotype VI is yet to be covered in the vaccine development program.