Mechanism of metronidazole resistance in Helicobacter pylori

OBJECTIVE: Drug resistance to Helicobacter pylori is one of the most important reasons for the failure of anti-H. pylori treatment. Metronidazole is a preferred drug for the elimination of H. pylori. However, using this drug alone can easily lead to resistance. The aim of the present study was to investigate the mechanism of metronidazole resistance in H. pylori. METHODS: International standard strain NCTC11639 was used. For the nitrate reduction test, four strains were used as positive controls, two strains of Bacillus coli and two strains of Vibrio cholerae. Metronidazole was used as tablets (0.2 g per tablet). The following techniques were used: (i) metronidazole used to apply selective pressure; (ii) sodium dodecylsulfate–polyacrylamide gel electrophoresis (SDS-PAGE); (iii) nitrate reduction test; and (iv) test to detect the enzyme activities associated with 95 different substrates for Gram-negative bacteria. RESULTS: As a result of the selective pressure of metronidazole, 20 H. pylori colonies survived; the bacteriostatic zones of these colonies were 0 mm in diameter, whereas the original NCTC11639 bacteriostatic zones were 25 mm in diameter. There was no significant difference seen among the 18 strains of drug-resistant H. pylori and the original NCTC11639 strain protein electrophoresis strips. In the nitrate reduction test, both sensitive and resistant H. pylori all tested negative and the control strains of Bacillus coli and Vibrio cholerae tested positive. After the mutation of H. pylori from sensitive to resistant, the activities of enzymes associated with mono-methyl succinate, succinic acid and D-alanine metabolism were decreased, and those associated with L-fucose and 6-phosphate glucose metabolism were increased. CONCLUSIONS: The resistance of H. pylori to metronidazole is not related to nitroreductase. There may be no obvious changes in membrane protein in the drug-resistant strain. The metronidazole resistance of H. pylori is associated with its metabolism and a change in enzyme activities.