Antibacterial efflux systems.

Drug efflux, unidirectional pumping of cytotoxic drugs, is a major mechanism of antimicrobial multiresistance in bacteria. Although these efflux systems are usually chromosomally encoded, some are present on plasmids. Some of the efflux pumps are relatively well known: Emr and Acr system in Escherichia coli, whose outer membrane protein seems to be the multifunctional To1C; the mex efflux system described in Pseudomonas aeruginosa and ABC-type in Gram-negative bacteria. Also the role of efflux in Gram-positive bacteria are reviewed including Bacillus, Staphylococcus and Streptomyces.