Variation of the mexT gene, a regulator of the MexEF-OprN efflux pump expression in wild-type strains of Pseudomonas aeruginosa

We found three variations of wild-type strains in terms of mexT-mediated re gulation of the MexEF-OprN efflux pump, in which overexpression of the pump results in nfxC-type antibiotic resistance in Pseudomonas aeruginosa. Type -I: the mexT gene of the wild-type strain encoded inactive MexT and the nfx C-type mutants derived from this parent had an additional mutation in mexT converting MexT from the inactive to the active form. Type-II: The mexT gen e in the wild-type strain had an 8-bp insert producing inactive MexT and th e nfxC-type mutants from this parent had a deletion of the 8-bp insert conv erting inactive MexT to the active form. Type-III: Both the wild type strai n and its nfxC-type derivative produced identical and active MexT. The nfxC mutant from this parent must have an additional mutation. The original nfx C mutant isolated in 1990 might be derived from the Type-I parent strain. ( C) 2000 Federation of European Microbiological Societies. Published by Else vier Science B.V. All rights reserved.