The role of two-component system response regulator BceR in antimicrobial resistance, virulence, biofilm formation, and stress response of group B Streptococcus.

The hypervirulent Group B Streptococcus (Streptococcus agalactiae, GBS) serogroup III clonal cluster 17 has been associated with neonatal GBS invasive disease and meningits. Serogroup III, ST283 has recently been implicated in invasive disease among non-pregnant adults in Asia. These strains cluster with strains from freshwater fishes from aquaculture and a foodborne outbreak of sepsis, especially with septic arthritis, had been linked to such consumption in Singapore in 2015. Through comparative genome analyses of invasive and non-invasive strains of ST283, we identified a truncated response regulator gene in the non-invasive strain. This two component response gene, previously named a DNA binding regulator, is conserved among GBS strains and is a homologue of Bacillus subtilis BceR, the response regulator of the BceRSAB system. Loss of function of the BceR response gene in the invasive GBS strain demonstrated bacitracin susceptibility in{Delta} BceR mutant with MICs of 256-fold and four-fold reduction in bacitracin and human cathelicin LL-37 compared to wild type and complementation strains. Upregulation of dltA of wild type strain vs{Delta} BceR mutant was demonstrated (p<0.0001), and was previously shown in Staphylococcus aureus to resist and repel cationic peptides through excess positive charges with D-alanylation of teichoic acids on the cell wall. In addition,{Delta} BceR mutant was less susceptible under oxidative stress under H2O2 stress when compared to wild type strain (p<0.001) and inhibited biofilm formation (p<0.05 and p < 0.0001 for crystal violet staining and cfu counts). The{Delta} BceR mutant also showed reduced mortality as compared to wild type strain (p<0.01) in a murine infection model. Taken together, BceRS is involved in bacitracin and antimicrobial peptide resistance, survival under oxidative stress, biofilm formation and play an important role in the virulence of GBS.\n\nAuthor SummaryTwo-component systems (TCSs) play an important role in virulence in bacteria, and are involved in detecting environmental changes. Although S. agalactiae was reported to contain more predicted TCSs than Streptococcus pneumoniae, few have been studied in detail. In this work, comparative genomic analysis of GBS invasive (hyper-virulent) and non-invasive serotype III-4 strains were performed to determine any gene differences that may account for severity of disease in humans. BceR-like TCS was selected and suspected to be involved in virulence, and thus BceR was deleted in a hyper-virulent GBS serotype III-4 strain. We demonstrated that this BceR-like TCS is involved in GBS virulence and induced proinflammatory host immune responses. Our study of TCS BceR may guide further research into the role of other TCSs in GBS pathogenicity, and further explore therapeutic targets for GBS disease.