Multistate, Population-Based Distributions of Candidate Vaccine Targets, Clonal Complexes, and Resistance Features of Invasive Group B Streptococci Within the United States, 2015-2017

Background. Group B Streptococcus (GBS) is a leading cause of neonatal sepsis and meningitis and an important cause of invasive infections in pregnant and nonpregnant adults. Vaccines targeting capsule polysaccharides and common proteins are under development. Methods. Using whole genome sequencing, a validated bioinformatics pipeline, and targeted antimicrobial susceptibility testing, we characterized 6340 invasive GBS isolates recovered during 2015-2017 through population-based Active Bacterial Core surveillance (ABCs) in 8 states. Results. Six serotypes accounted for 98.4% of isolates (21.8% la, 17.6% V, 17.1% II, 15.6% III, 14.5% lb, 11.8% IV). Most (94.2%) isolates were in 11 clonal complexes (CCs) comprised of multilocus sequence types identical or closely related to sequence types 1, 8, 12, 17, 19, 22, 23, 28, 88,452, and 459. Fifty-four isolates (0.87%) had point mutations within pbp2x associated with nonsusceptibifity to 1 or more beta-lactam antibiotics. Genes conferring resistance to macrolides and/or lincosamides were found in 56% of isolates; 85.2% of isolates had tetracycline resistance genes. Two isolates carrying vanG were vancomycin nonsusceptible (minimum inhibitory concentration = 2 mu g/mL). Nearly all isolates possessed capsule genes, 1-2 of the 3 main pilus gene clusters, and 1 of 4 homologous alpha/Rib family determinants. Presence of the hvgA virulence gene was primarily restricted to serotype III/CC17 isolates (465 isolates), but 8 exceptions (7 IV/CC452 and 1 IV/CC17) were observed. Conclusions. This first comprehensive, population-based quantitation of strain features in the United States suggests that current vaccine candidates should have good coverage. The beta-lactams remain appropriate for first-line treatment and prophylaxis, but emergence of nonsusceptibifity warrants ongoing monitoring.

Automated summary

Based on a comprehensive study of invasive GBS in the United States, six serotypes accounted for the majority of isolates, with most isolates belonging to 11 clonal complexes. High rates of antibiotic resistance genes were found, suggesting the need for ongoing monitoring and the importance of vaccine coverage.