MexXY RND pump of Pseudomonas aeruginosa PA7 effluxes bi-anionic β-lactams carbenicillin and sulbenicillin when it partners with the outer membrane factor OprA but not with OprM

Abstract

Antibiotic resistance in <i>Pseudomonas aeruginosa</i> is a serious concern in healthcare systems. Among the determinants of antibiotic resistance in <i>P. aeruginosa</i>, efflux pumps belonging to the resistance-nodulation-division (RND) family confer resistance to a broad range of antibacterial compounds. The MexXY efflux system is widely overexpressed in <i>P. aeruginosa</i> isolates from cystic fibrosis (CF) patients. MexXY can form functional complexes with two different outer membrane factors (OMFs), OprA and OprM. In this study, using state-of-the-art genetic tools, the substrate specificities of MexXY-OprA and MexXY-OprM complexes were determined. Our results show, for the first time, that the substrate profile of the MexXY system from <i>P. aeruginosa</i> PA7 can vary depending on which OM factor (OprM or OprA) it complexes with. While both MexXY-OprA and MexXY-OprM complexes are capable of effluxing aminoglycosides, the bi-anionic β-lactam molecules carbenicillin and sulbenicillin were found to only be the substrate of MexXY-OprA. Our study therefore shows that by partnering with different OMF proteins MexY can expand its substrate profile.