[Resistance of Escherichia coli isolated from the urinary tract to amoxicillin-clavulanic acid and other antibiotics]

Abstract

Objective: The aim of this study was to determine the antimicrobial activity of amoxicillin-clavulanic acid against Escherichia coli urinary strains, especially those resistant to amoxicillin, and to analyze the results according to the susceptibility testing methods.

Method: This prospective study was made from April to May 2008, on 301 E. coli strains isolated from urine samples. The susceptibility to antibiotics was studied by agar disk diffusion according to French Society of Microbiology Antibiogram Committee recommendations. MIC were determined with the E-test.

Results: According to the antibiogram, 59.8% of strains were resistant to amoxicillin, 33.2% to amoxicillin-clavulanic acid, 1.7% to cefotaxim, 8.3% to nalidixic acid, 6.6% to ofloxacin, 4.7% to ciprofloxacin, 4.7% to gentamicin and 38.1% to cotrimoxazole. After determining the MIC of E. coli strains resistant to amoxicillin and susceptible to amoxicillin-clavulanic acid, 37.5% (n=30) remained susceptible, 61.25% (n=55) were of intermediate susceptibility and only one strain (1.25%) was resistant. Among E. coli strains resistant to amoxicillin and intermediately susceptible to amoxicillin-clavulanic acid, 83.3% (n=55) remained intermediately susceptible, 13.7% (n=9) became susceptible and two strains (3%) were resistant.

Conclusion: The susceptibility testing methods, especially for amoxicillin-clavulanic acid, must be standardized to avoid the discrepancies noted between standard antibiograms and an accurate determination of MIC.