Relationship Between mexB Efflux Pump Gene Expression, Efflux Pump Activity and Biofilm Formation in Multidrug Resistant Clinical Isolates of Pseudomonas Aeruginosa

Pseudomonas aeruginosa is an opportunistic gram-negative pathogen, causing life threatening nosocomial infections including respiratory system, urinary system and skin wounds (1). P. aeruginosa exhibits resistance to a range of antibiotic classes, including aminoglycosides, carbapenems, beta-lactams, quinolones, and cephalosporins (2). Frequent occurrence of drug resistance is due to many virulence factors in P. aeruginosa such as flagella, pili, lipopolysaccharides, secreted enzymes like DNase and lipase, toxins, and pigments as pyocyanin which play crucial roles in tissue damage and immune suppression. Multiple resistant mechanisms are developed by P. aeruginosa (3). Two prominent mechanisms, biofilm formation and efflux pump activity among other mechanisms, play an important role in persistence and antibiotic resistance (4). Biofilm formation produced by P. aeruginosa is a complex phenomenon that promotes antibiotic resistance and shields the pathogen from the host immune system. This results in severe clinical outcomes in critically ill patients (5). There are about 12 resistance-nodulation-division (RND) families of efflux pumps in P. aeruginosa. The mexAB-oprM multidrug efflux pump system of P. aeruginosa is involved in resistance (6). Efflux pumps play a role in biofilm formation by influencing Physical-chemical interactions, mobility, gene regulation, quorum sensing (QS), extracellular polymeric substances (EPS), and toxic compound extrusion (6)(7). It has been demonstrated that MexAB-OprM plays a role in the resistance of aztreonam, gentamicin, tetracycline and tobramycin in biofilm structures of P. aeruginosa (8). MexB is the most critical and specific gene for efflux activity within the MexAB-OprM system and contributes to antibiotic resistance in Pseudomonas aeruginosa (9).