Role of Mexl in Pseudomonas Aeruinosa Mexj Efflux Operon Expression.

摘要

The purpose of this study was to determine the regulatory mechanism(s) of a hitherto uncharacterized resistance nodulation cell division (RND) efflux pump, MexJK, in Pseudomonas aeruginosa. The clinical significance of this efflux pump has not been determined. However, it is widely accepted that RND efflux pumps in conjunction with P. aeruginosa's low permeability barrier significantly contribute to its intrinsic resistance to antibiotics, and this bacterium is therefore considered one of the most important nosocomial disease causing agents of our time. A gene encoding a protein belonging to the tetracyline repressor family of proteins (PA3678) and designated mexL is divergently transcribed from and located 94 bp upstream of the mexJK operon. It is my contention that MexL represses the MexJK efflux pump by binding via its putative helix-turn-helix motif on or before the promoter-containing region of the mexJK operon. A chromosomal delta mexL mutant named PAO318 was engineered from a mexAB-oprM and mexCD-oprJ double knockout mutant, PAO238. Phenotypic characterization of PAO318 by minimum inhibitory concentration (MIC) tests, revealed that PAO318 was resistant to resistant at >128 micrograms/ml. Furthermore, complementation of PAO318 with a plasmid born mexL reduced the MIC for resistant to 20 micrograms/ml, which is consistent with the MIC of the susceptible parent strain, PAO238. To quantitate transcriptional repression by MexL, lacZ operon fusions were constructed with the mexJK operon promoter. The beta-Galactosidase activity observed in these strains suggest that MexL represses the expression of mexJK by at least 4 fold.