Evolving antimicrobial resistance patterns in group B streptococci: A five-year study in a high-risk pregnancy...

Streptococcus agalactiae (commonly referred to as group B streptococci [GBS]) is a leading cause of neonatal infection. Surveillance of colonization in pregnant women and the use of intrapartum antibiotic prophylaxis (IAP) are the primary strategies for preventing early-onset GBS disease. The increasing rate of antibiotic resistance among GBS isolates is a concern for the effectiveness of IAP. Our study aimed to evaluate the prevalence of GBS colonization and characterize antimicrobial resistance patterns over a five-year period in a high-risk pregnancy referral center in Northeastern Brazil.

This study was conducted from 2020 to 2024 and included pregnant women at 35-37-week gestation. GBS isolates from anal-vaginal swabs were identified and tested for susceptibility to penicillin or ampicillin, clindamycin, erythromycin, levofloxacin, and tetracycline. Isolates stored from 2021 to 2024 were further analyzed for the resistance genes mef(A), erm(A/TR), erm(B), tet(M), and tet(O).

Of 1469 anal-vaginal samples, the overall GBS colonization rate was 12%. All isolates were susceptible to either penicillin or ampicillin. The respective resistance rates for erythromycin, clindamycin, levofloxacin, and tetracycline were 23.6%, 9.3%, 5.4%, and 82.3%. The main determinant among macrolide-resistant isolates was mef(A), and tet(M) was the most frequent tetracycline resistance gene. Furthermore, we found that erythromycin resistance increased consistently over the five years, signaling a potential impact on clindamycin efficacy due to erm genes.

Beta-lactams (penicillin and ampicillin) remained effective for IAP in northeastern Brazil during the study period. However, high and increasing resistance to other antibiotic classes reinforces the need for maternal GBS surveillance and ongoing antimicrobial resistance monitoring.