Prevalence, Serotype Distribution, and Antimicrobial Resistance of Streptococcus agalactiae Among Pregnant Women in Greece: A Retrospective Study

Background: Streptococcus agalactiae (group B Streptococcus, GBS) remains a leading cause of invasive infections in pregnant women, fetuses, and neonates. Universal screening at 36-37 weeks of gestation followed by intrapartum antibiotic prophylaxis is essential to prevent adverse outcomes. However, data on GBS serotype distribution are limited in several regions, including Greece. This study aimed to determine the prevalence, serotype distribution, and antimicrobial susceptibility of GBS isolates among pregnant women in Greece. Methods: Vaginal and rectal swabs were collected from pregnant women undergoing routine GBS screening between January 2021 and December 2025. Samples were processed using selective enrichment broth and cultured on blood agar and chromogenic media. Identification was based on standard microbiological methods, CAMP test, and VITEK2 system. Antimicrobial susceptibility testing and macrolide-lincosamide-streptogramin B (MLSB) phenotyping were performed. Serotyping was conducted using a commercial latex agglutination assay. Results: Among 941 women screened, 118 (12.5%) were colonized with GBS. The most prevalent serotypes were III (29.7%), V (18.6%), Ib (14.4%), IX (10.2%), Ia (9.3%), and II (9.3%). All isolates were susceptible to penicillin. Resistance to erythromycin and clindamycin was observed in 29.7% and 22.9% of isolates, respectively. The predominant MLSB phenotype was constitutive (cMLSB, 78.4%), followed by inducible (iMLSB, 13.5%), L (5.4%), and M (2.7%) phenotypes. Conclusions: GBS colonization was detected in 12.5% of pregnant women, with serotype III predominating, underscoring its clinical relevance due to its association with invasive neonatal disease. Although penicillin remains fully effective, the observed resistance to macrolides and lincosamides, primarily mediated by the cMLSB phenotype, raises concerns regarding alternative therapies.