Group B Streptococcus capsular serotype alters vaginal colonization fitness.
J Infect Dis 2021;
225:1896-1904. [PMID:
34788438 DOI:
10.1093/infdis/jiab559]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2021] [Accepted: 11/02/2021] [Indexed: 11/12/2022] Open
Abstract
BACKGROUND
Group B Streptococcus (GBS) remains a leading cause of infant morbidity and mortality. A candidate vaccine targets six GBS serotypes, offering a potential alternative to intrapartum antibiotic prophylaxis to reduce disease burden. However, our understanding of the contributions of specific capsule types to GBS colonization and disease remains limited.
METHODS
Using allelic exchange, we generated isogenic GBS strains differing only in the serotype-determining region in two genetic backgrounds, including the hypervirulent clonal complex (CC) 17. Using a murine model of vaginal co-colonization, we evaluated the roles of the presence of capsule and of expression of specific capsular types in GBS vaginal colonization fitness independent of other genetic factors.
RESULTS
Encapsulated wild-type strains COH1 (CC17, serotype III) and A909 (non-CC17, serotype Ia), outcompeted isogenic acapsular mutants in murine vaginal co-colonization. COH1 wild-type outcompeted A909. Notably, expression of type Ia capsule conferred an advantage over type III capsule in both genetic backgrounds.
CONCLUSIONS
Specific capsule types may provide an advantage in GBS vaginal colonization in vivo. However, success of certain GBS lineages, including CC17, likely involves both capsule and non-capsule genetic elements. Capsule switching in GBS, a potential outcome of conjugate vaccine programs, may alter colonization fitness or pathogenesis.
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