METRONIDAZOLE AND CLARITHROMYCIN RESISTANCE IN HELICOBACTER-PYLORI DETERMINED BY MEASURING MICS OF ANTIMICROBIAL AGENTS IN COLOR INDICATOR EGG-YOLK AGAR IN A MINIWELL FORMAT

Resistance of Helicobacter pylori to metronidazole often causes failur e of commonly used combination drug treatment regimens, We determined the MICs of metronidazole and clarithromycin against 18 H. pylori stra ins from Peru using tetrazolium egg yolk (TEY) agar, The MIC results o btained by agar dilution with petri dishes were compared with the resu lts found through a miniwell format, The results of the two protocols for measuring drug susceptibility differed by no more than 1 dilution in all cases, On TEY agar, bright-red H. pylori colonies were easy to identify against a yellow background, Sixty-one percent (11 of 18) of the strains were resistant to metronidazole (MIC, greater than or equa l to 4 mu g/ml) and 50% (9 of 18) were resistant to clarithromycin (MI C, greater than or equal to 0.125 mu g/ml), whereas none (0 of 5) of t he strains tested were resistant to tetracycline (MIC, greater than or equal to 1 mu g/ml). Thus, the prevalence of metronidazole and clarit hromycin resistance in Peru is higher than that In developed regions o f the world, The miniwell plate with TEY agar allows easy H. pylori co lony identification, requires about one-third less of the costly mediu m necessary for petri dish assaying, conserves space, and yields MICs equivalent to those with agar dilution in petri dishes.