F2F Poster 21st Lancefield International Symposium for Streptococci and Streptococcal Diseases 2022

Background

Streptococcus agalactiae (group B streptococci, GBS) is primarily of microbiota of the genitourinary and gastrointestinal tracts. GBS lineages colonizing pregnant women are well studied but less is known about non-pregnant adult colonization. We characterized GBS colonization in adults as a potential reservoir for infections and tested for the presence of clones with a potentially higher invasive disease potential.

Methods

We evaluated GBS colonization among 336 non-pregnant adults in the community and compared it with contemporary invasive isolates (n=268). All isolates were characterized by serotyping, multilocus sequence typing, surface protein gene and pili profiling, and antimicrobial susceptibility.

Results

The colonization rate (32%) among non-pregnant adults increased with age, potentially explaining the higher incidence of disease with older age.

The diversity of the 268 invasive disease isolates in terms of serotype and ST was similar to those of colonizing GBS, despite non-significant differences in serotype distribution, even when stratifying by age.

The serotype Ib/CC1 was the dominant lineage in colonization (23%) and invasive disease (26%), a lineage shown to result from a capsular switching event. Comparison of contemporary isolates did not reveal any lineage significantly more represented in either asymptomatic carriage or invasive disease in Portugal (Figure).

Conclusions

Asymptomatic colonization of non-pregnant is significant and could act as a reservoir for invasive disease. We found a similar distribution of serotypes and genetic lineages in contemporary colonizing and invasive disease isolates, consistent with GBS acting as an opportunistic pathogen with no particularly virulent lineages for adult infections, in contrast to infant disease.