Metronidazole susceptibility testing of Helicobacter pylori with the PDM epsilometer test (E test)

The bacteriostatic activity of metronidazole against Helicobacter pylori was determined with the PDM epsilometer test (E test) and with an agar dilution test. Both methods correlated in the minimum inhibitory concentration (MIC) ranges (< or = 0.5- > 32 mg/l) and in the MIC 50 (E test: 1 mg/l; agar dilution test: 2 mg/l) and MIC 90 (> 32 mg/l) values. However, comparison of test results of single strains revealed that 14 out of 105 strains (13.3%) were classified as resistant by one method but classified susceptible by the other. The correlation coefficient of 0.71 also indicated a low congruence of test results. It is concluded that both methods should be used in order to ascertain all strains resistant to metronidazole.