ROLE OF THE MULTIDRUG EFFLUX SYSTEMS OF PSEUDOMONAS-AERUGINOSA IN ORGANIC-SOLVENT TOLERANCE

Multidrug efflux pumps with a broad substrate specificity make a major contribution to intrinsic and acquired multiple antibiotic resistance in Pseudomonas aeruginosa. Using genetically defined efflux Pump muta nts, we investigated the involvement of the three known efflux systems , MexA-MexB-OprM, MexC-MexD-OprJ, and MexE-MexF-OprN, in organic solve nt tolerance in this organism. Our results showed that all three syste ms are capable of providing some level of tolerance to organic solvent s such as n-hexane and p-xylene. Expression of MexAB-OprM was correlat ed with the highest levels of tolerance, and indeed, this efflux syste m was a major contributor to the intrinsic solvent tolerance of P. aer uginosa. Intrinsic organic solvent tolerance was compromised by a prot onophore, indicating that it is substantially energy dependent. These data suggest that the efflux of organic solvents is a factor in the to lerance of P. aeruginosa to these compounds and that the multidrug eff lux systems of this organism can accommodate organic solvents, as well as antibiotics.