Analysis of the roles of the regulatory systems VicRK and CovR in antibiotic resistance of Streptococcus mutans and Streptococcus sanguinis

Abstract

Streptococcus mutans and Streptococcus sanguinis are ubiquitous species of the dental biofilms, commonly involved in opportunistic cardiovascular infections, such as infective endocarditis (IE). There is evidence that systemic infections promoted by these bacteria involve a restricted sub-set of strains with increased expression of virulence genes, as consequence of spontaneous mutations in the genes encoding for the transcription regulatory systems VicRK and CovR. These systems are highly conserved among Gram positive bacteria, and regulate genes for cell wall biogenesis and virulence. Interestingly, natural mutants of gene encoding for VicRK (vicR, vicK) are recovered in vitro, after bacterial exposure to antibiotics targeting the cell wall. Therefore, the aim of this project is to investigate the roles of VicRK and CovR in the resistance of S. mutans and S. sanguinis strains to antibiotics applied to control streptococcal EI. To that purpose, a total of twenty seven strains of these species (20 isolated from the oral cavity and 9 isolated from the bloodstream) will be analyzed regarding their susceptibility to seven antibiotics (penicillin, amoxicillin, erythromycin, doxycycline, vancomycin and daptomycin) in assays for determination of the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (CBM). The profiles of antibiotic resistance will be then compared with polymorphisms in the vicR, vicK and/or covR to be assessed in in silico analysis of the genomes of the S. sanguinis strains, and already identified in previous studies of S. mutans strains. The sensitivity to these drugs will be also compared between knockout mutants of vicK or covR, obtained in reference strains of S. mutans (UA159) and S. sanguinis (SK36). The results of this project might contribute for elucidating the roles of VicRK and CovR regulatory systems in the resistance of S. mutans and S. sanguinis to antibiotics applied to control IE. Moreover, the results might help on studies addressing the role of antibiotictherapy in the emergence of hypervirulent strains evolved from natural mutations in vicRK and covR.