The rdxA gene plays a more major role than frxA gene mutation in high-level metronidazole resistance of Helicobacter pylori in Taiwan

Background. Metronidazole-resistant H. pylori associating with mutations of rdxA or frxA is still a debated topic. This study investigates whether rdxA and frxA mutations of H. pylori accounted for the high MIC value (≥ 64 µg/ml) of metronidazole (Mtz). Material and Methods. From 126 clinical H. pylori isolates, we examined 14 Mtz-sensitive, 18 Mtz-resistant H. pylori, and eight pairs of Mtz-sensitive and Mtz-resistant colonies simultaneously present within a single gastric biopsy. The paired strains from one single biopsy were proven identical by PCR-RFLP. MICs of Mtz were checked by the E-test and agar dilution method. The mutations of rdxA and frxA sequencing were matched with the Mtz-susceptible ATCC 26695 and J99. Results. There were 89% (16/18) of Mtz-resistant isolates with mutation of RdxA. Half of the 14 Mtz-sensitive strains, all without mutation of RdxA, still contained truncation of FrxA. Within the paired isolates from a single biopsy, rdxA mutation (86%) was more common than frxA mutation (43%) in those isolates with high-level Mtz-resistant H. pylori. RdxA truncation was more prevalent in Mtz-resistant strains with high MICs than in those with low to moderate MICs (75% vs. 20%, p = .01, OR: 12, 95% CI: 1.8–81.7). Conclusion. Mutations in the rdxA gene rather than the frxA gene generally determine a high MIC level of Mtz-resistant H. pylori in Taiwan.