Study of rdxA and frxA genes mutations in metronidazole resistant and susceptible Helicobacter pylori clinical isolates from the central region of Portugal

Abstract Objectives Helicobacter pylori is one of the most prevalent global pathogens and colonizes an estimated 50% of the world’s population. Although metronidazole is an important antibiotic playing a relevant role in different H. pylori eradication therapies, its frequent consumption results in increased resistance frequencies with a consequent negative impact on the treatment efficacy. Mutations on genes encoding NADPH nitroreductases, commonly known as rdxA gene (oxygen-insensitive) and frxA gene (flavinreductase) have been associated to H. pylori resistance to metrodinazole. The aim of this study was to evaluate the mutation profile of rdxA and frxA genes in a population of 38  H. pylori isolates with phenotypic patterns of susceptibility and resistance to this antibiotic. Methods “Touchdown” PCR with the purpose of amplifying rdxA and frxA genes in one PCR was used. Sequence data were made by pair-wise sequence alignment and were examined in terms of codons and comparison was achieved regarding amino acids. Results Although repeated mutations occurred in positions 118, 131, 172, and 183 of rdxA , and in 72, 73, 110, 126 and 193 of frxA gene, it must be highlighted that mutations are widespread along these two genes in this population. Furthermore, 6 metrodinazole resistant isolates did not present any mutation on frxA gene. Conclusions This work seems to confirm that mutations on rdxA and frxA genes alone are unable to justify metrodinazole resistance in H. pylori isolates and additional mechanisms may exist and should be investigated.