Vaccine Targets and Antimicrobial Resistance of <i>Streptococcus agalactiae</i> Recovered From Pregnant Women in Brazil

OBJECTIVES: The available measure to prevent Streptococcus agalactiae (Group B Streptococcus, GBS) neonatal infection is intrapartum antibiotic prophylaxis (IAP), but it is threatened by bacterial resistance. Therefore, this study aimed to investigate antimicrobial resistance and bacterial targets of vaccines at the most advanced stage of development. METHODS: GBS isolates (n = 222) recovered from pregnant women between 2019 and 2024 were subjected to capsular polysaccharides and alpha-like proteins investigation and antimicrobial susceptibility testing. Macrolide and fluoroquinolone resistance determinants and genetic diversity of multidrug-resistant (MDR) isolates were also investigated. RESULTS: The main capsular types were Ia (78, 35.1%), III (42, 18.9%), V (39, 17.6%) and II (32, 14.4%). Vaccines based on hexavalent capsular polysaccharides and alpha-like proteins would have 97.3% and 87.5% of predicted efficacy, respectively. Isolates were categorized as not susceptible (NS), that is, intermediate and resistant, to levofloxacin (5, 2.3%), clindamycin (11, 5%), erythromycin (58, 26.1%) and tetracycline (171, 77%). Among erythromycin NS isolates, the M phenotype/mef(A) gene predominated (47, 81%). All levofloxacin-resistant isolates showed amino acid substitutions in both GyrA (S81L) and ParC (S79F). MDR isolates (10, 4.5%) had distinct genetic backgrounds. CONCLUSIONS: Both immunization approaches would be effective in the population. Although the elevated erythromycin resistance rate, one of the highest reported in the country, clindamycin remains an efficient option in IAP. MDR isolates have not resulted from the dissemination of a single clone, but instead showed a polyclonal origin.