title: beta-Lactam coselection of sensitive and TEM-1 beta-lactamase-producing subpopulations in heterogeneous Escherichia coli colonies.
abstract: We tested the effect of different concentrations of cefamandole, cefotaxime, cefoxitin and imipenem on homogeneous and heterogeneous bacterial stationary colonies. A reduction of not more than 100-fold in the bacterial colony population was obtained with sensitive Escherichia coli K12 strains. When an E. coli strain producing high levels of TEM-1 beta-lactamase constituted 6% or more of the population, the whole colony was resistant to cefamandole, but still sensitive to cefotaxime, cefoxitin or imipenem. Thus in the case of cefamandole the sensitive subpopulation is co-selected by the resistant one. It is suggested that the occurrence of resistant subpopulations, as a small part of an apparently sensitive E. coli population, can lead to therapeutic failures with beta-lactamase-sensitive agents.
mesh_terms: D000900:Anti-Bacterial Agents / Q000378:metabolism* / Q000494:pharmacology; D004352:Drug Resistance, Microbial; D004926:Escherichia coli / Q000187:drug effects / Q000201:enzymology*; D008826:Microbial Sensitivity Tests; D010957:Plasmids; D013379:Substrate Specificity; D001618:beta-Lactamases / Q000096:biosynthesis*; D047090:beta-Lactams
chemical_list: D000900:Anti-Bacterial Agents; D047090:beta-Lactams; D001618:beta-Lactamases