Discrepancies between E-Test and Agar Dilution Methods for Testing Metronidazole Susceptibility of Helicobacter pylori

We read with interest the recently published paper by Piccolomini et al. (7). They evaluated three different methods to study the susceptibility of Helicobacter pylori to 20 antimicrobial agents. They found a very good correlation between E-test and agar dilution methods, as well as between broth microdilution and agar dilution. They recommended the E test as a reliable and alternative method for testing susceptibility of H. pylori to a wide range of antimicrobial agents in clinical practice. However, they found six major errors (6 of 71, 8.5%) and two very major errors (2 of 71, 2.8%) with the metronidazole E tests when they compared the results with those obtained by reference methods. They consider that chance is the explanation for why these errors were observed only with metronidazole.