Frame-shift mutations in NAD(P)H flavin oxidoreductase encoding gene (frxA) from metronidazole resistant Helicobacter pylori ATCC43504 and its involvement in metronidazole resistance

Metronidazole is a critical ingredient for combination therapies of Helicob acter pylori infection, the major cause of peptic ulcer and gastric cancer. It has been recently reported that metronidazole resistance from H. pylori ATCC43504 is caused by the insertion of a mini-IS605 sequence and deletion of sequences in an oxygen insensitive NAD(P)H nitroreductase encoding gene (rdxA). We also found that an additional gene (frxA) encoding NAD(P)H flav in oxidoreductase in the same strain was truncated by frame-shift mutations . To assess whether the frxA truncation is also involved in metronidazole r esistance, metronidazole sensitive H. pylori strains ATCC43629 and SS1 were transformed by the truncated frxA gene cloned from strain ATCC43504. All t ransformed cells grew on agar plates containing 16 mu g ml(-1) of metronida zole. The involvement of the frxA gene in metronidazole resistance was also confirmed by insertion inactivation of frxA and/or rdxA genes from strain ATCC43629 and one metronidazole sensitive clinical isolate H. pylori 2600. In addition, the frxA gene cloned from the H. pylori 2600 showed metronidaz ole nitroreductase activity in Escherichia coli and rendered ordinary metro nidazole resistant E. coli to metronidazole sensitive cell. These results i ndicate that the frxA gene may also be involved in metronidazole resistance among clinical H. pylori isolates. (C) 2000 Federation of European Microbi ological Societies. Published by Elsevier Science B.V. All rights reserved.