Genetic diversity and antimicrobial resistance of invasive, noninvasive and colonizing group B Streptococcus isolates in southern Brazil

Introduction: Group B Streptococcus (GBS) is a human commensal bacterium that is also associated with infection in pregnant and non-pregnant adults, neonates and elderly people.

Gap statement: The authors hypothesize that knowledge of regional GBS genetic patterns may allow the use of prevention and treatment measures to reduce the burden of streptococcal disease.

Aim: The aim was to report the genotypic diversity and antimicrobial sensitivity profiles of invasive, noninvasive urinary and colonizing GBS strains, and evaluate the relationships between these findings.

Methodology: The study included consecutive and non-duplicated GBS isolates recovered in southern Brazil from 2015 to 2017. We performed multiple-locus variable-number tandem repeat analysis (MLVA) and PCR analyses to determine capsular serotypes and identify the presence of the resistance genes mefA/E, ermB and ermA/TR, and also antibiotic susceptibility testing.

Results: The sample consisted of 348 GBS strains, 42 MLVA types were identified, and 4 of them represented 64 % of isolates. Serotype Ia was the most prevalent (42.2 %) and was found in a higher percentage associated with colonization, followed by serotypes V (24.4 %), II (17.8 %) and III (7.8 %). Serotype V was associated with invasive isolates and serotypes II and III with noninvasive isolates, without significant differences. All isolates were susceptible to penicillin. GBS 2018/ hvgA was observed in 17 isolates, with 11 belonging to serogroup III. The Hunter-Gaston diversity index was calculated as 0.879. The genes mefA/E, erm/B and erm/A/TR were found in 45, 19 and 46 isolates.

Conclusion: This report suggests that the circulating GBS belong to a limited number of genetic lineages. The most common genotypes were Ia/MT12 and V/MT18, which are associated with high resistance to macrolides and the presence of the genes mefA/E and ermA/TR. Penicillin remains the antibiotic of choice. Implementation of continuous surveillance of GBS infections will be essential to assess GBS epidemiology and develop accurate GBS prevention, especially strategies associated with vaccination.