Frameshift mutations in frxA occur frequently and do not provide a reliable marker for metronidazole resistance in UK isolates of Helicobacter pylori

Abstract

Mutations in the NAD(P)H flavin oxidoreductase gene (frxA) are thought to contribute to the development of metronidazole resistance inHelicobacter pylori. To test this further, 44frxAsequences in 18 patient isolate sets ofH. pyloriwere examined including a unique collection comprising separated Mtz-sensitive (MtzS) and Mtz-resistant (MtzR) subpopulations pre-treatment and matched MtzRstrains post-treatment. Sequences offrxAcontained frameshift mutations that led to premature protein truncation in at least one strain from most (17/18) patient sets. These mutations were present in all strains, irrespective of Mtz resistotype in 13/18 patients. Frameshift due to a single adenine deletion at nucleotide 53 was the most common mutation and was present in isolates from 11/18 patients. A novel real-time (LightCycler) PCR-based probe hybridization melting-point assay applied to a further 119 isolates confirmed that the frameshift-53 mutation occurred frequently, in 20 % of isolates, and could be present in MtzSas well as MtzRstrains (42 % vs 58 %). This study demonstrates that frameshift mutations occur in MtzSstrains as well as in MtzRstrains, and are thus unlikely to cause Mtz resistance.