title: Contribution of efflux to cefuroxime resistance in clinical isolates of Escherichia coli.
abstract: Retrospective data showed that resistance to cefuroxime among clinical blood culture isolates of Escherichia coli (2.67%) was more common than resistance to cefotaxime (0.59%) and ceftazidime (1.48%). 30 clinical isolates of E. coli with various degrees of resistance to cefuroxime were selected for the present studies. Antibiotic susceptibility to beta-lactam antibiotics was determined with the disc-diffusion method and for cefuroxime also with the E-test. The ability to grow in the presence of organic solvents was determined as a phenotypical measure of efflux. The organic solvent tolerance (OST) was graded on a scale from 1 to 5. Antibiotic susceptibility to cefuroxime, cefotaxime, ceftazidime and loracarbef was also determined in the presence of a known efflux pump inhibitor, MC-207,110. The strains that were organic solvent tolerant had significantly higher minimal inhibitory concentration (MIC) values for cefuroxime than the other E. coli strains (median 24 mg/l, range 4 to > 256 mgn/l vs median 4 mg/l, range 2-64 mg/l) and significantly lower cefuroxime zone diameters (p < 0.02). In the strains with most pronounced organic solvent tolerance, i.e. the cyclohexane-tolerant strains, the cefuroxime MIC values were decreased 2-fold (p < 0.03) and the zone diameters increased (p < 0.02) by the addition of an efflux pump inhibitor, MC-207,110. The findings supported the hypothesis that efflux contributes to cefuroxime resistance in E. coli.
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001425:Bacterial Outer Membrane Proteins / Q000494:pharmacology*; D002439:Cefotaxime / Q000494:pharmacology*; D003470:Culture Media; D004347:Drug Interactions; D004352:Drug Resistance, Microbial; D004926:Escherichia coli / Q000187:drug effects* / Q000302:isolation & purification*; D005260:Female; D006801:Humans; D008297:Male; D008826:Microbial Sensitivity Tests; D012680:Sensitivity and Specificity; D018709:Statistics, Nonparametric; D013548:Sweden; D001618:beta-Lactamases / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D001425:Bacterial Outer Membrane Proteins; D003470:Culture Media; D001618:beta-Lactamases; D002439:Cefotaxime