title: Selection of resistant mutants of Citrobacter freundii by second and third-generation cephalosporins and imipenem.
abstract: Using a single-step selection procedure, resistant mutants could be obtained from three clinical isolates of Citrobacter freundii with two second-generation and four third-generation cephalosporins but not with imipenem. All mutants showed a drastically increased beta-lactamase activity and were cross-resistant to all the cephalosporins examined. Combinations of cloxacillin with the cephalosporins were markedly synergistic, suggesting the principal role of the cephalosporinase in the resistance of these mutants.
mesh_terms: D002511:Cephalosporins / Q000494:pharmacology*; D002954:Citrobacter / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D004352:Drug Resistance, Microbial; D006801:Humans; D015378:Imipenem; D009154:Mutation; D013845:Thienamycins / Q000494:pharmacology*; D001618:beta-Lactamases / Q000235:genetics
chemical_list: D002511:Cephalosporins; D013845:Thienamycins; D015378:Imipenem; D001618:beta-Lactamases