Cooperation between Alteration of DNA Gyrase Genes and Over‐Expression of MexB and MexX Confers High‐Level Fluoroquinolone Resistance in Pseudomonas aeruginosa Strains Isolated from a Patient Who Received a Liver Transplant Followed by Treatment with Fluoroquinolones

Abstract

Clinical isolates of highly fluoroquinolone-resistant Pseudomonas aeruginosa had a mutation in either A or B subunit of DNA gyrase and over-expressed MexB and MexX, the efflux system proteins. Introduction of wild-type gyrase genes of Escherichia coli into the isolates made them as fluoroquinolonesusceptible as the moderately fluoroquinolone-resistant strains that only over-expressed efflux system proteins. These findings demonstrate that high fluoroquinolone-resistance in P. aeruginosa is attributed to cooperation between alteration in DNA gyrase genes and over-expression of efflux systems proteins.