Hypoxia Increases Antibiotic Resistance in Pseudomonas aeruginosa through Altering the Composition of Multidrug Efflux Pumps

Abstract

ABSTRACTAntibiotic resistance is a significant and developing problem in general medical practice and a common clinical complication in cystic fibrosis patients infected withPseudomonas aeruginosa. Such infections occur within hypoxic mucous deposits in the cystic fibrosis lung; however, little is known about how the hypoxic microenvironment influences pathogen behavior. Here we investigated the impact of hypoxia on antibiotic resistance inP. aeruginosa. The MICs of a selection of antibiotics were determined forP. aeruginosagrown under either normoxic or hypoxic conditions. The expression of mRNAs for resistance-nodulation-cell division (RND) multidrug efflux pump linker proteins was determined by real-time PCR, and multidrug efflux pump activity was inhibited using Phe-Arg β-naphthylamide dihydrochloride. The MIC values of a subset of clinically importantP. aeruginosaantibiotics were higher for bacteria incubated under hypoxia than under normoxia. Furthermore, hypoxia altered the stoichiometry of multidrug efflux pump linker protein subtype expression, and pharmacologic inhibition of these pumps reversed hypoxia-induced antibiotic resistance. We hypothesize that hypoxia increases multidrug resistance inP. aeruginosaby shifting multidrug efflux pump linker protein expression toward a dominance of MexEF-OprN. Thus, microenvironmental hypoxia may contribute significantly to the development of antibiotic resistance inP. aeruginosainfecting cystic fibrosis patients.