Contribution of efflux to cefuroxime resistance in clinical isolates of Escherichia coli.
SCANDINAVIAN JOURNAL OF INFECTIOUS DISEASES(2009)
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 mg/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.
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Key words
escherichia coli
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