Overexpression of the MexXY Multidrug Efflux System Correlates with Deficient Pyoverdine Production in .

Multidrug-resistant poses a serious problem due to hospital- and healthcare-associated infections. A major drug resistance mechanism of involves active efflux via resistance nodulation cell division (RND)-type multidrug efflux pumps of which MexXY is increasingly recognized as a primary determinant of aminoglycoside resistance in . MexXY overexpression is often observed in drug-resistant clinical isolates. MexXY deficiency increased pyoverdine production in all four strains we tested. MexXY-overproducing multidrug-resistant PA7 exhibited the greatest effect among the strains. Complementation with a MexXY-expressing plasmid restored low-level pyoverdine production in a MexXY-deficient mutant from PA7, indicating that MexXY expression decreases pyoverdine production. Because produces pyoverdine to acquire iron, MexXY-deficient mutants might be more susceptible to iron deficiency than MexXY-producing strains or might require extra iron. High-risk clones of multidrug-resistant reportedly tend to be MexXY overproducers but defective pyoverdine producers. This study suggests that reduces production of a virulence factor after acquiring a drug resistance factor.