Mechanism of Antimicrobial Sensitivity of Streptococcus mutans

Abstract

The quorum sensing system of Streptococcus mutans is mediated by the competence stimulating peptide CSP, whose precursor is encoded by the comC gene. A comC mutant of strain GS 5 exhibited enhanced antimicrobial sensitivity to a wide variety of different agents. However, the addition of exogenous CSP did not complement this phenotype, thus it was determined that increased tetracycline sensitivities resulted from the repression of the putative bacteriocin immunity protein gene bip, which is located immediately upstream from comC. We also found that inactivation of bip or smbG, other bacteriocin immunity protein genes present within the smb operon in S. mutans GS 5, affected antimicrobial sensitivity to a variety of antimicrobial agents. Furthermore, both the bip and smbG genes were upregulated in the presence of low concentrations of tetracycline, and also induced during biofilm formation relative to planktonic cells. These results are the first to show that the antimicrobial sensitivity of a bacterium can be modulated by some of the putative bacteriocin immunity proteins expressed by the organism.