Contribution of multidrug efflux pumps to multiple antibiotic resistance in veterinary clinical isolates of Pseudomonas aeruginosa

The contribution of efflux pumps to multidrug resistance in 12 Pseudomonas aeruginosa isolates from various animal sources was assessed. Western immunoblot analyses demonstrated that all twelve isolates expressed significant levels of the MexAB OprM efflux system whereas two isolates simultaneously expressed the MexEF OprN or MexXY systems, respectively. One strain contained a single mutation in mexR, a regulator of mexAB-oprM expression, that did not adversely affect the MexR amino acid sequence, and three isolates contained the same, single base change in the mexA-mexR intergenic region. The MexXY-expressing strain contained two base substitutions in its mexZ regulatory gene which did not alter the MexR sequence.