Two Efflux Systems Expressed Simultaneously in Multidrug-Resistant Pseudomonas aeruginosa

Abstract
Simultaneous overexpression of MexAB-OprM and MexEF-OprN was demonstrated for a multiply antibiotic-resistant clinical isolate of Pseudomonas aeruginosa (G49). G49 also had decreased expression of OprF. No mutations in mexR or its upstream promoter region, mexT , oprM , oprF , or sigX were revealed, suggesting regulation by a hitherto undescribed locus.