Influence of the MexAB-OprM multidrug efflux system on quorum sensing in Pseudomonas aeruginosa

Abstract

Pseudomonas aeruginosa nalB mutants which hyperexpress the MexAB-OprM multidrug efflux system produce reduced levels of several extracellular virulence factors known to be regulated by quorum sensing. Such mutants also produce less acylated homoserine lactone autoinducer PAI-1, consistent with an observed reduction in lasI expression. These data suggest that PAI-1 is a substrate for MexAB-OprM, and its resulting exclusion from cells hyperexpressing MexAB-OprM limits PAI-1-dependent activation of lasI and the virulence genes.

FIG. 1

Production of AI-dependent virulence factors as a function of mexAB-oprM expression. P. aeruginosa K1171 (wild type [wt] for mexAB-oprM), K1168 (nalB), and K1169 (nalB ΔmexAB-oprM; ΔABM) were examined for the production of elastase (values reported have been multiplied by 100), casein protease (values reported have been multiplied by 10), and pyocyanin. Results reported are per milliliter of cells at an A₆₀₀ of 1.0 and are the means of the results of three separate experiments ± the standard deviations.

FIG. 2

AI production as a function of mexAB-oprM expression. PAI-1 (A) and PAI-2 (B) levels were measured in cell-free supernatants of 18-h cultures of P. aeruginosa K1171 (wild type for mexAB-oprM; wt), K1168 (nalB), and K1169 (nalB ΔmexAB-oprM; ΔABM) as described in the text. Values reported are the means of results from five separate experiments ± the standard deviations.

FIG. 3

β-Galactosidase activities of 18-h cultures of P. aeruginosa K1171 (wild type for mexAB-oprM; wt), K1168 (nalB), and K1169 (nalB ΔmexAB-oprM; ΔABM) harboring lasI-lacZ fusions. Values reported are the means of results from three separate experiments ± the standard deviations.