Comparison of the E test and agar dilution method for antimicrobial suceptibility testing of Helicobacter pylori

A multicentre study was carried out in order to validate the E test in comparison with the reference agar dilution method for testing the susceptibility of Helicobacter pylori to amoxicillin, clarithromycin, and metronidazole. Ten clinical isolates and one control collection isolate ( Helicobacter pylori ATCC 43504) were tested blindly at four centres according to a uniform methodology. The E test showed excellent intra- and inter-laboratory correlations with the agar dilution method for amoxicillin and clarithromycin (>98% agreement within 2 log(2) dilution steps). For metronidazole, however, the E test revealed significantly higher minimum inhibitory concentration values (>2 log(2)) against 5 of the 10 Helicobacter pylori strains tested. Overall, neither method was found reliable for testing the susceptibility of Helicobacter pylori to metronidazole, since both tended to lack reproducibility.