Influence of mutations in the mexR repressor gene on expression of the MexA-MexB-OprM multidrug efflux system of Pseudomonas aeruginosa

Several nalB-type multidrug-resistant mutants of Pseudomonas aeruginosa ove rexpressed MexAB-OprM and carried mutations in the total regulatory gene, m exR. Others, dubbed nalC types, carried mutations elsewhere and overexpress ed MexAB-OprM less extensively than the nalB strains. Available evidence sh owed that MexR acted solely as repressor. Disruption of the mexR gene at va rious places suggested that the 5' end of mexR may be a part of the mexAB-o prM promoter.