title: Physico-chemical factors affect chloramphenicol efflux and EmhABC efflux pump expression in Pseudomonas fluorescens cLP6a.
abstract: Protein synthesis inhibitors such as chloramphenicol and tetracycline may be inducers of efflux pumps such as MexY in Pseudomonas aeruginosa, complicating their use for the treatment of bacterial infections. We previously determined that chloramphenicol, a substrate of the EmhABC efflux pump in Pseudomonas fluorescens cLP6a, did not induce emhABC expression. In this study, we determined the effect of physico-chemical factors on chloramphenicol efflux by EmhABC, and the expression of emhABC. Efflux assays measuring accumulation of (14)C-chloramphenicol in cell pellets showed that chloramphenicol efflux is dependent on growth temperature, pH and concentration of Mg(2+). These physico-chemical factors modulated the efflux of chloramphenicol by 26 to >50%. All conditions tested that decreased the efflux of chloramphenicol unexpectedly induced transcription of emhABC efflux genes. EmhABC activity also effectively suppressed the deleterious effect of chloramphenicol on the cell membrane of strain cLP6a, which may explain why chloramphenicol is not an inducer of emhABC. Our results suggest that the detrimental effect of an antibiotic on cell membrane integrity and fatty acid composition may be the signal that induces emhABC expression, and that inducers of other bacterial efflux pumps may include environmental factors rather than their substrates per se.
authors.affiliation: Department of Biological Sciences, CW405 Biological Sciences Center, University of Alberta, Edmonton, Alberta, Canada T6G 2E9. adebusuy@ualberta.ca
authors.forename: Abigail
authors.initials: A
authors.lastname: Adebusuyi
authors.forename: Julia
authors.initials: J
authors.lastname: Foght
mesh_terms: D000900:Anti-Bacterial Agents / Q000378:metabolism*; D001693:Biological Transport, Active; D002462:Cell Membrane / Q000187:drug effects; D002701:Chloramphenicol / Q000378:metabolism*; D005227:Fatty Acids / Q000378:metabolism; D020869:Gene Expression Profiling; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism*; D011551:Pseudomonas fluorescens / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism* / Q000528:radiation effects; D013696:Temperature; D014158:Transcription, Genetic
chemical_list: D000900:Anti-Bacterial Agents; D005227:Fatty Acids; D026901:Membrane Transport Proteins; D002701:Chloramphenicol; D008274:Magnesium