title: Sequential inactivation of rdxA (HP0954) and frxA (HP0642) nitroreductase genes causes moderate and high-level metronidazole resistance in Helicobacter pylori.
abstract: Helicobacter pylori is a human-pathogenic bacterial species that is subdivided geographically, with different genotypes predominating in different parts of the world. Here we test and extend an earlier conclusion that metronidazole (Mtz) resistance is due to mutation in rdxA (HP0954), which encodes a nitroreductase that converts Mtz from prodrug to bactericidal agent. We found that (i) rdxA genes PCR amplified from 50 representative Mtz(r) strains from previously unstudied populations in Asia, South Africa, Europe, and the Americas could, in each case, transform Mtz(s) H. pylori to Mtz(r); (ii) Mtz(r) mutant derivatives of a cultured Mtz(s) strain resulted from mutation in rdxA; and (iii) transformation of Mtz(s) strains with rdxA-null alleles usually resulted in moderate level Mtz resistance (16 microg/ml). However, resistance to higher Mtz levels was common among clinical isolates, a result that implicates at least one additional gene. Expression in Escherichia coli of frxA (HP0642; flavin oxidoreductase), an rdxA paralog, made this normally resistant species Mtz(s), and frxA inactivation enhanced Mtz resistance in rdxA-deficient cells but had little effect on the Mtz susceptibility of rdxA(+) cells. Strains carrying frxA-null and rdxA-null alleles could mutate to even higher resistance, a result implicating one or more additional genes in residual Mtz susceptibility and hyperresistance. We conclude that most Mtz resistance in H. pylori depends on rdxA inactivation, that mutations in frxA can enhance resistance, and that genes that confer Mtz resistance without rdxA inactivation are rare or nonexistent in H. pylori populations.
authors.affiliation: Department of Molecular Microbiology and Department of Genetics, Washington University Medical School, St. Louis, Missouri 63110, USA.
authors.forename: J Y
authors.initials: JY
authors.lastname: Jeong
authors.forename: A K
authors.initials: AK
authors.lastname: Mukhopadhyay
authors.forename: D
authors.initials: D
authors.lastname: Dailidiene
authors.forename: Y
authors.initials: Y
authors.lastname: Wang
authors.forename: B
authors.initials: B
authors.lastname: Velapatiño
authors.forename: R H
authors.initials: RH
authors.lastname: Gilman
authors.forename: A J
authors.initials: AJ
authors.lastname: Parkinson
authors.forename: G B
authors.initials: GB
authors.lastname: Nair
authors.forename: B C
authors.initials: BC
authors.lastname: Wong
authors.forename: S K
authors.initials: SK
authors.lastname: Lam
authors.forename: R
authors.initials: R
authors.lastname: Mistry
authors.forename: I
authors.initials: I
authors.lastname: Segal
authors.forename: Y
authors.initials: Y
authors.lastname: Yuan
authors.forename: H
authors.initials: H
authors.lastname: Gao
authors.forename: T
authors.initials: T
authors.lastname: Alarcon
authors.forename: M L
authors.initials: ML
authors.lastname: Brea
authors.forename: Y
authors.initials: Y
authors.lastname: Ito
authors.forename: D
authors.initials: D
authors.lastname: Kersulyte
authors.forename: H K
authors.initials: HK
authors.lastname: Lee
authors.forename: Y
authors.initials: Y
authors.lastname: Gong
authors.forename: A
authors.initials: A
authors.lastname: Goodwin
authors.forename: P S
authors.initials: PS
authors.lastname: Hoffman
authors.forename: D E
authors.initials: DE
authors.lastname: Berg
mesh_terms: D019943:Amino Acid Substitution; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002701:Chloramphenicol / Q000494:pharmacology; D004352:Drug Resistance, Microbial / Q000235:genetics*; D016480:Helicobacter pylori / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics* / Q000302:isolation & purification; D006801:Humans; D008795:Metronidazole / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests; D016296:Mutagenesis; D016297:Mutagenesis, Site-Directed; D009601:Nitroreductases / Q000235:genetics* / Q000378:metabolism; D017384:Sequence Deletion
chemical_list: D000900:Anti-Bacterial Agents; D008795:Metronidazole; D002701:Chloramphenicol; C029492:aromatic NADH-dependent nitroreductase; D009601:Nitroreductases; C413454:flavin nitroreductase