Expression of the las and rhl quorum-sensing systems in clinical isolates of Pseudomonas aeruginosa does not correlate with efflux pump expression or antimicrobial resistance

OBJECTIVES: Quorum-sensing systems regulate expression of several virulence factors and may affect the MexAB-OprM efflux system in Pseudomonas aeruginosa. This study investigated the relationship between two quorum-sensing systems, efflux pump MexAB-OprM expression and antimicrobial resistance in 33 clinical isolates of P. aeruginosa. METHODS: Expression of the quorum-sensing regulatory genes lasR and rhlR was assessed by real time RT-PCR. The autoinducer synthetase genes lasI and rhlI and the regulatory genes mexT and mexS were characterized by DNA sequencing. Production of pyocyanin and elastase in each of the isolates was also determined. RESULTS: While there was a significant correlation between expression of the quorum-sensing regulatory genes and production of pyocyanin and elastase, there was no correlation with expression of mexA or with antimicrobial resistance. There were no mutations in lasI, rhlI, mexT or mexS that correlated with quorum-sensing expression. CONCLUSIONS: Increased activity of two quorum-sensing systems in P. aeruginosa does not contribute to increased mexA expression or antimicrobial resistance.