[Antibiotic resistance caused by membrane impermeability and multidrug efflux systems]

Multiple antibiotic resistance(MDR) in bacteria was at first thought to be caused exclusively by the combination of several resistance mechanisms including membrane impermeability, the outer membrane barrier in gram-negative bacteria. More recently, it became clear that MDR are often achieved by interplay between impermeability and multidrug efflux pumps. Streptococcus pneumoniae MefA, Staphylococcus aureus NorA and Pseudomonas aeruginosa Mex of these pumps are significant, because those bacteria are more frequently isolated in clinical. In this review, we described on characteristics and clinical significance of P. aeruginosa Mex systems, MexA-MexB-OprM, MexC-MexD-OprJ, MexE-MexF-OprN and MexX-MexY-OprM, and furthermore, on interplay between the efflux systems, the outer membrane barrier, hydrolyzing enzyme and mutated target.