Population structure of group B Streptococcus from semen reveals virulent and resistant lineages with implications for surveillance

Group B Streptococcus (GBS) is a major agent of perinatal infections. Although extensively studied as a pathogen in pregnant individuals and neonates, little is known about GBS from male adults, despite occasional reports of its occurrence in semen. We characterized 120 GBS isolates obtained from semen samples in Brazil between 2017 and 2022 to determine serotypes, antimicrobial susceptibility profile, virulence-associated determinants, clustered regularly interspaced short palindromic repeats (CRISPR) diversity and phylogenetic relationships with isolates from other clinical sources. Serotype V was the most frequent, followed by Ia, Ib, III, II and IV. Resistance was observed for tetracycline (84.1%), erythromycin (30.8%), levofloxacin (8.3%) and 12.5% exhibited multidrug resistance (MDR). The most common sequence types (STs) were ST1, ST144 and ST19. The isolates clustered into five major clonal complexes (CC1, CC17, CC19, CC23 and CC24) and six singletons. Serotypes, antimicrobial resistance and virulence-associated determinants markers varied across CCs. Resistance determinants detected included tetM, mefA, msrD, ermA and ermB . Levofloxacin-resistant isolates contained mutations in gyrA and/or parC and were predominantly linked to the serotype V/ST19 lineage. All isolates except one carried at least one alpha-like protein (Alp) gene. Phylogenetic analysis of isolates from semen, rectovaginal samples, urine and invasive infections showed that isolates clustered according to CC regardless of clinical source. CRISPR1 analysis revealed intra-clonal diversity, as isolates within the same CC displayed different CRISPR compositions. These findings indicate that GBS isolates recovered from semen belong to established GBS lineages also identified in other clinical sources and support the co-circulation of GBS lineages across different human niches.