Streptococcus agalactiae is the leading cause of meningitis in newborns and a significant cause of invasive diseases in pregnant women and adults with underlying diseases. Antibiotic resistance against erythromycin and clindamycin in group B streptococcus (GBS) isolates has been increasing worldwide. GBS expresses the Srr1 and Srr2 proteins, which have important roles in bacterial infection. They have been investigated as novel vaccine candidates against GBS infection, with promising results. But a recent study detected non-srr1/2-expressing clinical isolates belonging to serotype III. Thus, we aimed to analyze the genotypes of non-srr1/2 GBS clinical isolates collected between 2013 and 2016 in South Korea. Forty-one (13.4%) of the 305 serotype III isolates were identified as non-srr1/2 strains, including sequence type 19 (ST19) (n = 16) and ST27 (n = 18) strains. The results of the comparative genomic analysis of the ST19/serotype III/non-srr1/2 strains further revealed four unique gene clusters. Site 4 in the srr1 gene locus was replaced by an lsa(E)-lnu(B)-aadK-aac-aph-aadE-carrying multidrug-resistant gene cluster flanked by two IS1216 transposases with 99% homology to the enterococcal plasmid pKUB3007-1. Despite the Srr1 and Srr2 deficiencies, whichresulted in reduced fibrinogen binding, the adherence of non-srr1/2 strains to endothelial and epithelial cells was comparable to that of Srr1-or Srr2-expressing strains. Moreover, their virulence in mouse models of meningitis was not significantly affected. Furthermore, additional adhesin-encoding genes, including a gene encoding a BspA-like protein, which may contribute to colonization by nonsrr1/2 strains, were identified via whole-genome analysis. Thus, our study provides important findings that can aid in the development of vaccines and antibiotics against GBS.
Bibliographical noteFunding Information:
This work was supported by the Nuclear R&D Program of the Ministry of Science and ICT (H.S.S.), the National Research Foundation of Korea (grant numbers NRF-2017M2A2A6A02020925 and NRF-2018K2A206023828 to H.S.S. and NRF-2018R1D1A1B07048399 to J.H.L.), and the Ministry of Food and Drug Administration (grant number 18172MFDS253 to J.Y.S.). The funders had no role in the study design, data collection and interpretation, or the decision to submit the work for publication.
© 2021. Zhi et al. This is an openaccess article distributed under the terms of the Creative Commons Attribution 4.0 International license.
- Streptococcus agalactiae
- multidrug resistance gene