Isolation and Evaluation of Pilli Genes in Group B Streptococcus Isolated from Vaginal Samples

Streptococcus agalactiae (Group B Streptococcus, GBS) continues to be an important colonizer and opportunistic pathogen in women with a growing focus on its potential virulence factors and changing antibiotic resistance profiles. Pili structures described by pilus island genes such as pi1 and pi2 are important factors for adhesion, colonization, and immune evasion and may be associated with trends of antimicrobial resistance. The study assessed the prevalence of pi1 and pi2 genes in S. agalactiae isolates retrieved from vaginal samples and its association with resistance against frequently used antibiotics in Iran. From the vaginal swabs of women attending gynecologic clinics at Al-Sadr Medical City, Najaf, Iraq, 60 S. agalactiae isolates were collected between summer 2024 and early winter 2025. Bacterial identification was carried out using standard cultural and biochemical methods. The Kirby–Bauer disc diffusion method was used to perform antibiotic susceptibility testing for penicillin G, ampicillin, erythromycin, clindamycin, and cefotaxime. Conventional PCR was used for molecular detection of pilus genes pi1 and pi2. Gene carriage and antimicrobial resistance associations were explored using statistical analyses. Penicillin G and ampicillin had low resistance rates (5.0 and 6.7%, respectively), while higher resistance rates were associated with erythromycin (23.3%), clindamycin (16.7%), and cefotaxime (11.7%). Overall, pi1 gene and pi2 gene were detected in 66.7% and 75.0% of isolates, respectively. There were significant associations for all pilus genes and both macrolides and lincosamides where pi2 was a stronger association (p < 0.05) across a wider range of antibiotics. Molecular surveillance is warranted due to the high prevalence of pilus genes among vaginal S. agalactiae isolates together with significant associations with antimicrobial resistance. These data identify pili as epidemiological markers and underscore the importance of regionalized antimicrobial stewardship to minimize the spread of resistant GBS lineages.