A-038. Metronidazole Resistance Development Is Coupled with Down-Regulation of an Oxygen-Insensitive NAD(P)H Nitroreductase Encoding Gene (rdxA) in Helicobacter pylori

D. H. Kwon1, J. Wu2, H. Lu2, D. Y. Graham2;
1Long Island Univ., Brooklyn, NY, 2VA Med. Ctr. of Baylor Coll. of Med., Houston, TX.

Background &Aims: Helicobacter pylori is a human gastric pathogen causing peptic ulcer disease. Metronidazole is one of key anti-H. pylori drugs; the prevalence of metronidazole resistant H. pylori is currently very high and impairs successful treatment. Metronidazole is a prodrug required to be activated by nitroreductase from the host cell. A major resistance mechanism to this drug has been includes null mutations in a gene encoding oxygen-insensitive NAD(P)H nitroreductase (rdxA). To understand development of metronidazole resistance at the whole genome level transcriptomic studies were performed. Methods: Metronidazole resistant H. pylori was produced from H. pylori 26695 using different cell numbers and metronidazole concentrations. Total RNA was extracted from one of the metronidazole resistant strains grown with (8 μg/mL) or without metronidazole as well as from the parental strain and used for DNA microarray analyses. Selected genes from the strains including clinical isolates were studied by Northern and Immunoblot analyses. Results: Overall gene expression from an entire collection of H. pylori genes (1950 ORFs) was decreased 28% in the resistant strain grown without metronidazole and increased 21% in the resistant strain grown with metronidazole (compared to the parental strain). Comparisons of individual genes revealed 3 genes (rdxA, sodB, HP0954) were over 3-fold down-regulated in the resistant strain grown without metronidazole, but 45 and 28 genes were over 3-fold up-regulated and down-regulated, respectively, in the resistant strain grown with metronidazole. Down-regulation of the rdxA (5.0-fold) was present following growth with 2 μg/mL metronidazole as well as down-regulation of RdxA. Growth with 4 μg/mL showed absence of RdxA. Similarly, the rdxA was significantly decreased in metronidazole resistant clinical isolates as compared to those from the parental susceptible strains; the resistant clinical isolates had no RdxA. Conclusions: Development of metronidazole resistance is coupled with the down-regulation of rdxA in H. pylori