ANTIMICROBIAL SUSCEPTIBILITY TESTING OF HELICOBACTER-PYLORI - COMPARISON OF E-TEST, BROTH MICRODILUTION, AND DISK DIFFUSION FOR AMPICILLIN,CLARITHROMYCIN, AND METRONIDAZOLE

The optimal method for the determination of the minimum inhibitory con centration (MIC) of antimicrobials against Helicobacter pylori has not been established. The epsilometer agar diffusion gradient test (E-Tes t; AB Biodisk, Solna, Sweden) was compared with broth microdilution, t he reference method, and disk diffusion for the antimicrobial suscepti bility testing of 122 clinical isolates of H. pylori to ampicillin, cl arithromycin, and metronidazole. Isolates were considered to be resist ant when the MIC value was >8 mu g/ml for either ampicillin or metroni dazole and >2 mu g/ml for clarithromycin. For an individual isolate, t he MICs for ampicillin and clarithromycin determined by broth microdil ution and the E-test were highly reproducible, with replicate results being within +/-1 log(2) dilution. The correlation between the MICs de ter mined by E-test and broth microdilution was excellent for both amp icillin and clarithromycin (90.1% and 88.5% were within +/-log(2) dilu tion, and 98.3% and 96.7% of the values were within +/-2 log(2) diluti on, respectively). In no instance did the interpretation of ''sensitiv e'' or ''resistant'' differ. Conversely, only 70.5% of the E-test resu lts for metronidazole were within +/-1 log(2) dilution of the broth mi crodilution results. In addition, 15 (12.3%) of the H. pylori isolates interpreted as resistant by the E-test were sensitive by the broth mi crodilution method. All discrepancies occurred when the E-test MIC val ues fell between 8 and 32 mu g/ml. The results of the ampicillin and c larithromycin disk diffusion assay correlated 100% with the results of the broth microdilution. However, these data suggest that when the E- test MIC results for metronidazole yield values between 8 and 32 mu g/ ml, the MIC should be reevaluated by another method.