title: Accumulation of rifampicin by Escherichia coli and Staphylococcus aureus.
abstract: A centrifugation method was used to investigate the accumulation of 14C-rifampicin by Staphylococcus aureus and Escherichia coli, and to characterize the mechanism of rifampicin transport into S. aureus. For both species, drug accumulation was rapid with the steady-state concentration (SSC) reached within 40 s of drug exposure. Rifampicin accumulation by S. aureus was temperature and pH dependent; the lower the experimental temperature and the lower the experimental pH, the lower was the concentration of rifampicin accumulated. Accumulation was unaffected by the presence of inhibitors of antibiotic efflux, carbonyl cyanide m-chlorophenylhydrazone (CCCP), dinitrophenol (DNP), or reserpine. Exposure to increasing concentrations of rifampicin suggested that the accumulation process was saturable above a rifampicin concentration of 0.2 mg/L. Michaelis-Menten kinetics gave an apparent Km and Vmax for rifampicin, calculated from a Lineweaver-Burk plot, of 0.05 mg/L (0.06 microM) and 3.8 ng rifampicin per second, respectively. However, calculations suggest that these values reflect those for binding of rifampicin to its target, RNA polymerase.
authors.affiliation: Department of Infection, The Medical School, University of Birmingham, Edgbaston, UK.
authors.forename: K J
authors.initials: KJ
authors.lastname: Williams
authors.forename: L J
authors.initials: LJ
authors.lastname: Piddock
mesh_terms: D000904:Antibiotics, Antitubercular / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D015169:Colony Count, Microbial; D004140:Dinitrophenols / Q000494:pharmacology; D004926:Escherichia coli / Q000187:drug effects / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D012110:Reserpine / Q000494:pharmacology; D012293:Rifampin / Q000378:metabolism*; D013211:Staphylococcus aureus / Q000187:drug effects / Q000378:metabolism*; D013696:Temperature
chemical_list: D000904:Antibiotics, Antitubercular; D004140:Dinitrophenols; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D012110:Reserpine; D012293:Rifampin