Molecular studies of the LysR-type regulator, mexT and its regulation of the outer membrane porin protein OprD

Pseudomonas aeruginosa OprD is a specific porin which facilitates the uptake of basic amino acids and imipenem, a carbepenem antibiotic with high potency against P.aeruginosa. Resistance to imipenem occurs frequently during antibiotic therapy of patients with P.aeruginosa infections. This study was initiated to investigate the regulatory mechanisms in P.aeruginosa for the regulation of oprD. A putative LysR-type regulator, designated mexT, was cloned on a 1.2 kb PCR fragment. DNA sequencing predicted a 304 amino acid mature MexT protein. It showed strong homology to other LysR-type regulators. When overexpressed it induced expression of the mexEF-oprN efflux operon while repressing transcription of oprD. A second line of investigation was to try and identify conditions where this mexT gene might play a role in the regulation of its target genes in P.aeruginosa. Salicylate, an aromatic weak acid known to reduce porin expression and induce low levels of multiple antibiotic resistance in other bacteria, was found to reduce expression of oprD via transcription. No change in expression of any of the efflux operons was noted. Sodium benzoate, another aromatic weak acid, was shown to reduce the levels of OprD in the outermembranes of P.aeruginosa but the mechanism of reduction was found not to via transcription. Neither iron or zinc concentrations were found effect expression of oprD or any of the efflux operons. Finally, expression of these genes during growth phase was examined. No changes were noticed.Science, Faculty ofMicrobiology and Immunology, Department ofGraduat