Subinhibitory concentrations of the penicillin antibiotics induce quorum-dependent violacein synthesis in Chromobacterium violaceum

Abstract

The goal of the work was to analyze the ability of natural and semisynthetic penicillins to regulate the quorum sensing system in bacteria. The test strain was C. violaceum NCTC 13274 (CV 026) bearing mini-Tn5 insertion in the cviI gene that led to irreversible loss of N-acyl-L-homoserine lactone (AHL) biosynthesis and reversible suppression of violacein biosynthesis. Within the temperature range suboptimal for C. violaceum growth (17–22°C), subinhibitory concentrations of piperacillin, azlocillin, ticarcillin, carbenicillin, and oxacillin showed a quorum-dependent induction of violacein production, probably acting as AHL-mimetics. Cleavage of these antibiotics with beta-lactamase I and II led to the loss of both antibacterial and quorum-inducing activities. Inhibition of C. violaceum beta-lactamase by sulbactam resulted in manifestation of combined antibacterial and quorum-inducing activity of ampicillin and amoxicillin. These results improve our understanding of the role of beta-lactams and beta-lactamases in the processes of interspecific antagonism and in microbial intercellular communication.