DNA sequence analysis of rdxA and frxA from 12 pairs of metronidazole-sensitive and -resistant clinical Helicobacter pylori isolates

We previously reported that inactivation of rdxA and/or frxA converted Heli cobacter pylori from metronidazole sensitive to metronidazole resistant. To examine the individual roles of rdxA and frxA in the development of metron idazole resistance in H. pylori, we examined the status of rdxA and frxA fr om 12 pairs of metronidazole-sensitive and -resistant H. pylori isolates ob tained following unsuccessful therapy containing metronidazole. Arbitrary p rimed fingerprinting analyses revealed that the genotypes of 11 sensitive a nd resistant pairs of strains were essentially identical. Amino acid sequen ce identities of RdxA and FrxA from the 14 metronidazole-sensitive isolates ranged from 92 to 98% and 95 to 98%, respectively, compared to that of H. pylori J99 (MIC, 1 mug/ml). All strains with high-level metronidazole resis tance (MICs, 128 mug/ml) contained premature truncation of both RdxA and Fr xA caused by nonsense and/or frameshift mutations. Strains with intermediat e resistance to metronidazole (MICs, 32 to 64 mug/ml) contained a single pr emature truncation and/or altered RdxA and FrxA caused by nonsense, framesh ift, and unique missense mutations. The low-level metronidazole-resistant s trains (MICs, 8 mug/ml) contained unique missense mutations in FrxA but no specific changes in RdxA. The results demonstrate that alterations in both the rdxA and frxA genes are required for moderate and high-level metronidaz ole resistance and that metronidazole resistance that develops during anti- H. pylori therapy containing metronidazole is most likely to involve a sing le sensitive strain infection rather than a coinfection with a metronidazol e-resistant strain.