Open AccessnalB ‐type mutations causing the overexpression of the MexAB‐OprM efflux pump are located in the mexR gene of the Pseudomonas aeruginosa chromosome
Author(s) -
Saito Kohjiro,
Yoneyama Hiroshi,
Nakae Taiji
Publication year - 1999
Publication title -
fems microbiology letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.899
H-Index - 151
eISSN - 1574-6968
pISSN - 0378-1097
DOI - 10.1111/j.1574-6968.1999.tb08709.x
Subject(s) - biology , efflux , pseudomonas aeruginosa , operon , genetics , mutant , gene , mutation , wild type , microbiology and biotechnology , bacteria
Two mutations, one at the nalB and the other at the mexR locus, in the Pseudomonas aeruginosa chromosome are known to cause overexpression of the MexAB‐OprM efflux pump. Based on the following results, we concluded that nalB is the mutation that has occurred within the mexR gene of the P. aeruginosa chromosome. (i) Nucleotide sequencing of the mex operon upstream region of 21 independent nalB ‐type mutants including the original nalB9 revealed that all the mutations were located within the mexR gene. The mutations were classified into three different groups and nine types including single base substitutions, single base deletions and base insertions. (ii) Substitution of the mutant mexR with the wild‐type mexR and replacement of the wild‐type mexR with a defined mexR mutation resulted in the expression of wild‐type and nalB ‐type MexAB‐OprM respectively, which was confirmed by testing the antibiotic susceptibility and β‐galactosidase activity of the mexA‐lacZ translational fusion.