AI-2 quorum sensing affects antibiotic susceptibility in Streptococcus anginosus

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Abstract
The concern over rising antibiotic resistance necessitates exploration of alternative approaches in antimicrobial therapy. Bacterial communities use the auto-inducer 2 (AI-2) quorum sensing signal at a specific threshold level for intra- and interspecies communication in order to regulate virulence behaviour. AI-2 signal production occurs in bacteria that possess a luxS homologue. In this study, we investigate for the first time the association between AI-2 signalling and susceptibility to antibiotics. Streptococcus anginosus wild-type and its isogenic luxS mutant SA001 were exposed to erythromycin and ampicillin. Susceptibility to erythromycin and ampicillin was determined by measuring the cell density and viability. Complementation assays were conducted by exposing the mutant to wild-type supernatant or to the AI-2 precursor molecule dihydroxy-2,3-pentanedione (DPD). Disruption of luxS in S. anginosus resulted in a mutant with increased susceptibility to erythromycin and ampicillin. Supernatant from S. anginosus wild-type partially restored growth of SA001 in the presence of the two antibiotics. DPD restored growth of the luxS mutant in the presence of erythromycin and ampicillin to values similar to that of S. anginosus wild-type. Our results indicate that luxS-based AI-2 communication is associated with antibiotic susceptibility. Targeting the AI-2 signal communication may present a novel approach in antimicrobial therapy.