title: Accumulation of tetracyclines by Escherichia coli.
abstract: The net accumulation of tetracyclines by Escherichia coli as a function of concentration was shown to be biphasic. At concentrations less than the bacteriostatic levels, the mode of uptake was not azide-sensitive and was considered to be physical adsorption on the cell surface. At concentrations above the minimal inhibitory level, a second, azide-sensitive, uptake component was functional in addition to the surface adsorption process. This second energy-requiring mode was judged to represent penetration of the cytoplasmic membrane by tetracycline molecules to their sites of inhibitory action. Each mode for a given tetracycline and culture is expressed algebraically by a characteristic Freundlich equation. Resistance in E. coli is shown to be a result of diminished transport of antibiotic. However, this resistance was due not to a reduction or loss of a transport mechanism but rather to a requirement for higher antibiotic concentrations before the second mode of uptake could become operative.
mesh_terms: D000327:Adsorption; D001386:Azides / Q000494:pharmacology; D001692:Biological Transport; D002854:Chromatography, Paper; D004352:Drug Resistance, Microbial; D004926:Escherichia coli / Q000187:drug effects / Q000378:metabolism*; D005470:Fluorometry; D010118:Oxytetracycline / Q000378:metabolism; D013752:Tetracycline / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D001386:Azides; D013752:Tetracycline; D010118:Oxytetracycline