INNER MEMBRANE EFFLUX COMPONENTS ARE RESPONSIBLE FOR BETA-LACTAM SPECIFICITY OF MULTIDRUG EFFLUX PUMPS IN PSEUDOMONAS-AERUGINOSA

A major feature of the MexAB-OprM multidrug efflux pump which distingu ishes it from the MexCD-OprJ and MexEF-OprN multidrug efflux systems i n Pseudomonas aeruginosa is its ability to export a wide variety of be ta-lactam antibiotics. Given the periplasmic location of their targets it is feasible that beta-lactams exit the cell via the outer membrane OprM without interaction with MexA and MexB, though the latter appear to be necessary for OprM I function. To test this, chimeric MexAB-Opr J and MexCD-OprM efflux pumps were reconstituted in Delta mexCD Delta oprM and Delta mexAB Delta oprJ strains, respectively, and the influen ce of the exchange of outer membrane components on substrate (i.e., be ta-lactam) specificity was assessed. Both chimeric pumps were active i n antibiotic efflux as evidenced by their contributions to resistance to a variety of antimicrobial agents, although there was no change in resistance profiles relative to the native pumps, indicating that OprM is not the determining factor for the beta-lactam specificity of MexA B-OprM. Thus, one or both of inner membrane-associated proteins MexA a nd MexB are responsible for drug recognition, including recognition of beta-lactams.