Potential involvement of several nitroreductases in metronidazole resistance in Helicobacter pylori

Susceptibility of Helicobacter pylori to the antibiotic metronidazole has b een attributed to the activity of an oxygen-insensitive NADPH-dependent nit roreductase (RdxA), with resistance to this antimicrobial arising from null mutations in rdxA. To obtain a better understanding of the factors involve d in resistance, nitroreductase and metronidazole reduction activities were investigated in matched pairs of clinical and laboratory-derived sensitive and resistant H. pylori strains. Significant differences in enzyme activit ies were observed between sensitive and resistant strains, suggesting that metronidazole susceptibility in H. pylori was associated with more than one enzyme activity. To establish the mutations occurring in rdxA, the genes f rom seventeen bacterial strains, including matched pairs were sequenced. To assess whether metronidazole was responsible for inducing random mutations in this gene, the complete nucleotide sequence of gene hp0630, encoding an NAD(P)H-quinone reductase which also has NADPH-dependent nitroreductase ac tivity, was determined in the same strains. All resistant strains showed no nsense, missense, or frameshift mutations randomly throughout rdxA. In cont rast, no mutations were observed in hp0630. The results confirmed the prese nce of rdxA null mutations in resistant strains and suggested that other fa ctors involved in the metabolism of metronidazole contributed to the resist ant phenotype. (C) 2001 Academic Press.