INVITRO ACTIVITY OF METRONIDAZOLE AGAINST HELICOBACTER-PYLORI AS DETERMINED BY AGAR DILUTION AND AGAR DIFFUSION

Metronidazole activity against 25 clinical isolates of Helicobacter pylori was evaluated by agar dilution, epsilometer (E-test; AB Biodisk, Solna, Sweden), and disk diffusion methods after 3 and 5 days of incubation in a microaerophilic atmosphere. Agar dilution, performed in duplicate, provided reproducible results with MICs for 50 % of the isolates of less-than-or-equal-to 0.12-mu-g/ml after 3 and 5 days of incubation and MICs for 90 % of the isolates of 2 and 4-mu-g/ml after 3 and 5 days of incubation, respectively. Reproducibility of MICs was slightly better after 5 days than after 3 days of incubation. MICs obtained with the E-test were higher, with 76 and 68 % of isolates inhibited by less-than-or-equal-to 16-mu-g of metronidazole per ml after 3 and 5 days, respectively, in contrast with corresponding values of 92 and 88 % for agar dilution. Zone diameters obtained with the commercially available 80-mu-g metronidazole elution disk were too large (greater-than-or-equal-to 41 mm) to allow discrimination between susceptible and resistant isolates, although resistant subpopulations were detected by the appearance of inner colonies in four isolates. In conclusion, the E-test was easy to perform and interpret, and it appeared to be more likely than agar dilution to detect metronidazole resistance in vitro in H. pylori.