A comparison of the mechanisms of decreased susceptibility of aztreonam-resistant and ceftazidime-resistant Enterobacteriaceae

Research output: Contribution to journalArticle

Authors

Colleges, School and Institutes

Abstract

Twenty five strains of Enterobacteriaceae (five each of Enterobacter cloacae, Citrobacter freundii, Serratia marcescens, Morganella morganii and Providencia stuartii) were exposed to aztreonam and ceftazidime at 1/2 and 1 x MIC in liquid medium for 22 h, and also to 3, 5 and 10 x MIC and 16 mg/l of each agent in agar. Any putative mutant with an increase in the MIC of greater than or equal to 4 fold was examined for beta-lactamase expression and outer membrane protein profile. Mutants were selected on agar at approximately 10(7); however in liquid medium not all strains yielded mutants. Mutants lacking an outer membrane protein (OMP) with a molecular weight of 40,000 (+/- 5000) were selected with both agents, as were mutants expressing constitutive Richmond and Sykes Class 1 beta-lactamase. For the Ent. cloacae mutants increased beta-lactamase gave rise to MICs above the breakpoint of both agents, whereas with the other species ceftazidime susceptibility was more affected. Strains that were OMP- rarely had MICs above the breakpoint, unless there was also increased beta-lactamase expression, as in species such as M. morganii. Hence the major mechanism of resistance in these strains would appear to be beta-lactamase mediated rather than due to altered expression of outer membrane proteins.

Details

Original languageEnglish
Pages (from-to)749-62
Number of pages14
JournalJournal of Antimicrobial Chemotherapy
Volume26
Issue number6
Publication statusPublished - Dec 1990

Keywords

  • Aztreonam, Bacterial Outer Membrane Proteins, Ceftazidime, Culture Media, Drug Resistance, Microbial, Electrophoresis, Polyacrylamide Gel, Enterobacteriaceae, Microbial Sensitivity Tests, Molecular Weight, Mutation, Phenotype, beta-Lactamases