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 and intrapartum antimicrobial prophylaxis are essential to prevent adverse outcomes. 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 GBS screening between January 2021 and December 2025. Samples were processed using Todd-Hewitt broth with colistin and nalidixic acid, and cultured on blood agar and chromogenic media. The VITEK2 system was used for GBS identification and antimicrobial susceptibility testing against penicillin, erythromycin, clindamycin, tetracycline, levofloxacin, and vancomycin, according to EUCAST guidelines. The double-disk diffusion test was used for macrolide-lincosamide-streptogramin B (MLSB) phenotyping. Serotyping for all ten serotypes 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/or clindamycin was detected in 37 isolates. In these isolates, 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.