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Antimicrobial Agents and Chemotherapy, 09 1995, 1948-1953, Vol 39, No. 9
XZ Li, H Nikaido and K Poole
We have earlier described mexA-mexB-oprK, an operon involved in pyoverdine
export in Pseudomonas aeruginosa, and suggested that the products of these
genes also contribute to the active efflux of several antibiotics (K.
Poole, K. Krebes, C. McNally, and S. Neshat, J. Bacteriol. 175:7363-7372,
1993). Recently the outer membrane component of this efflux system was
shown to be OprM, rather than OprK (N. Gotoh and K. Poole, unpublished
results). In the present study, the conclusion concerning the efflux
activity of this system was confirmed and extended by the measurement of
drug accumulation in intact cells. Thus, the steady-state accumulation
levels of tetracycline and norfloxacin were increased in mexA and oprM null
mutants. mexA and oprM null mutants also showed an increase in
susceptibility to a wide variety of beta-lactam antibiotics and an increase
in the steady-state accumulation level of benzylpenicillin, indicating that
the MexA-MexB- OprM pump also effluxes beta-lactams. Furthermore,
deenergization of the cytoplasmic membrane with a proton conductor always
produced a strong increase in the accumulation level. Finally, a
single-step mutant over-producing MexAB-OprM accumulated less tetracycline
and chloramphenicol than the parent strain and was more resistant to a wide
range of antimicrobial compounds, including beta-lactams. These results
support the notion that these proteins contribute to the intrinsic
resistance of P. aeruginosa through the multidrug active efflux process.
Copyright © 1995 by the American Society for Microbiology. All rights reserved.
Role of mexA-mexB-oprM in antibiotic efflux in Pseudomonas aeruginosa
Department of Molecular and Cell Biology, University of California, Berkeley 94720, USA.
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