The E-Test and Campylobacter jejuni

Abstract

The E-Test is a recently introduced method for performing antimicrobial susceptibility tests. We compared the E-Test to the broth microdilution test and to the standard agar dilution test by using five antimicrobial agents tested against 55 clinical isolates of Campylobacter jejuni from 11 locations in USA (group 1). Later, we selected 30 strains (group 2), which were more resistant than the original survey isolates. Erythromycin, tetracycline, and ciprofloxacin were tested on both groups of organisms. When the three test methods were compared with each other at ±1 log 2 dilution, the E-test gave the best overall agreement, with 85% of all strains being within acceptable limits. Category interpretation of erythromycin (drug of choice) results was a problem using current NCCLS guideline breakpoints. For the E-Test and the agar dilution method, 82% of the strains were in the intermediate category; but with the broth microdilution method, only 16.4% of the isolates were interpreted as intermediate. If the susceptible category breakpoint was raised to ≤2 μg/ml, then only 3% of the C. jejuni isolates would be interpreted as intermediate by any of the three methods. Our preference for antimicrobial susceptibility testing of C. jejuni is either E-Test or agar dilution at 42°C for 16 hr.