Streptococcus agalactiae (Group B Streptococcus – GBS) is a relevant public health pathogen associated with severe infections in neonates, pregnant women, and immunocompromised individuals. Screening for maternal colonization, adoption of prophylactic measures, and control of antimicrobial resistance are essential for disease prevention. This study aimed to characterize GBS strains using phenotypic and molecular methods, evaluate antimicrobial resistance, and develop a diagnostic tool based on qPCR-HRM (quantitative PCR High-Resolution Melting).

Sixty-nine GBS strains from different clinical sites in the state of Rio de Janeiro between 2018 and 2024 were analyzed, including urine (n = 29), vaginal secretion (n = 26), anorectal (n = 3), urethral (n = 1), prostatic (n = 1), tracheal (n = 1), umbilical stump (n = 1), cerebrospinal fluid (n = 1), and unidentified clinical samples (n = 7). Phenotypic identification involved the CAMP test, sodium hippurate hydrolysis, and hemolysis analysis. Capsular serotyping was performed by latex agglutination, and molecular identification by MALDI-TOF MS and qPCR-HRM, with a primer adapted to the groEL gene.

Most isolates (90%) showed typical beta-hemolysis, while 3.33% exhibited hyper-hemolysis, weak hemolysis, or absence of hemolysis. The most prevalent serotypes were III (36%), V (26%), and Ia (16%). The qPCR-HRM method demonstrated high sensitivity, with 68 of 69 samples (≈98%) positive for the groEL-3F gene. Regarding resistance profile, tetracycline had the highest rate (≈73%), followed by erythromycin (≈20%), clindamycin (≈5%), and levofloxacin (≈5%). No penicillin- or vancomycin-resistant strains were observed, but seven strains showed inducible clindamycin resistance (D-test) and five were classified as multidrug-resistant (MDR).

The data obtained in this study not only demonstrate the presence of clinically relevant antimicrobial resistance among clinical GBS strains, but also reveal levofloxacin resistance rates higher than those previously described in the literature. These results suggest a concerning trend of increasing and spreading resistance among GBS isolates. In addition, they reinforce the importance of continuous GBS monitoring, highlighting qPCR-HRM as a promising tool for rapid and specific diagnosis.