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  • Title: Study of in vitro selected resistance of Pseudomonas aeruginosa to cefoperazone, ceftazidime, azthreonam and imipenem.
    Author: Van der Auwera P, Husson M, Bulliard G.
    Journal: Drugs Exp Clin Res; 1986; 12(11):871-83. PubMed ID: 3102194.
    Abstract:
    Ten strains of Pseudomonas aeruginosa were plated on agar containing cefoperazone, ceftazidime, azthreonam or imipenem alone and in combination with ampicillin or cefoxitin as inducers, and/or amikacin (MIC/4), according to Szybalsky. Regrowing colonies were randomly selected for MIC and MBC determinations. The numbers of regrowing colonies were occasionally increased by a beta-lactamase inducer, although amikacin significantly reduced it. Some 243 colonies were further studied. The most frequent phenotypes of resistance (195 mutants) were: resistance to cefoperazone, ceftazidime, azthreonam (99 regrowing colonies); resistance to cefoperazone, azthreonam (36); resistance to cefoperazone (17); resistance to cefoperazone, ceftazidime, azthreonam, imipenem (17). A total of 28/31 R mutants retained their phenotype after 15 subcultures in antibiotic-free medium. The mutants R cefoperazone, ceftazidime, azthreonam were studied by quantitative beta-lactamase evaluation in agar with substrate and non-substrate antibiotics, substrate profile study spectrophotometrically, crypticity study by comparing beta-lactamase activity of intact and sonicated cells spectrophotometrically, isoelectric focusing of sonicate extracts and dialysis experiments for trapping evaluation. These mutants were characterized by a 240-fold increase in beta-lactamase production (Pi = 8.7) and unchanged permeability. beta-lactamase trapping was demonstrated but could not explain alone the phenotype of resistance. These studies suggest that mutants constitutive for beta-lactamase production were easily selected in vitro. Amikacin was able significantly to prevent their emergence.
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