Resistance to the nitroheterocyclic drugs

Townson, Steven M.; Boreham, P. F. L.; Upcroft, Peter; Upcroft, Jacqueline

doi:10.1016/0001-706x(94)90062-0

Cited by 84 publications

(55 citation statements)

References 121 publications

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“…Soluble fractions of 7: fiietus, however, when supplemented with NADH or NADPH, were able to reduce nitrofurans but not metronidazole. Previous studies in this laboratory have shown that metronidazole activation was catalysed by Giardia ferredoxin in assays supplemented with PFOR and ferredoxin (Townson et al, 1994a) and that a decrease in PFOR activity correlated with drug resistance Townson et al, 1994b;Townson et al, 1996). However, a decrease in NADH oxidase activity does not appear to be a mechanism of resistance in several of our furazolidone-resistant Giardia lines (Townson et al, 1992) as determined by activity gel assays (data not shown).…”

Section: Discussionmentioning

confidence: 51%

A H₂O‐Producing NADH Oxidase from the Protozoan Parasite Giardia Duodenalis

Brown

Upcroft

1996

European Journal of Biochemistry

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We describe the purification of a H,O-producing NADH oxidase from the protozoan parasite Giardiu duodenalis. The enzyme is a monomeric flavoprotein containing flavin adenine dinucleotide in a 1 : 1 molar ratio with the polypeptide. The NADH oxidase has an apparent molecular mass of 46 kDa and was homogenous as determined by denaturing gel electrophoresis and N-terminal amino acid sequencing. NADPH could substitute for NADH as an electron donor with a K, value of 4.2 pM for NADH and 16 pM for NADPH (pH 7.8 at room temperature). With oxygen as the primary electron acceptor under aerobic conditions, the pure enzyme did not produce 0;-nor H,O, as stoichiometric products of oxygen reduction, implicating H,O as the end product and obviating the need for superoxide dismutase. The ability to utilise oxygen explains the apparent respiration of the amitochondrial fermentative metabolism of Giardia. Mercurials, flavoantagonists and heavy metals (CU'+ and ZnZ+ ) inhibited this activity. Under anaerobic conditions the enzyme catalysed electron transfer at lower efficiencies to other electron acceptors including nitroblue tetrazolium, potassium ferricyanide, FAD and FMN, using either NADH or NADPH as electron donors. NADPH, however, was a more efficient electron donor. Cytochrome c was not reduced under any assay conditions used. The enzyme reduced the nitrofuran drugs, furazolidone (an antigiardial) and nitrofurantoin, to their toxic radical forms as determined by EPR. Metronidazole, a nitroimidazole, was not reduced. Pure NADH oxidase did not demonstrate ferredoxin:NAD(P) ' oxidoreductase activity since it could not accept electrons from reduced ferredoxin to regenerate NAD(P)H. The G. duodenalis NADH oxidase may, therefore, function as a terminal oxidase, similar to the mitochondria1 cytochrome oxidase, and in the maintenance of an optimum intracellular redox ratio. This report of a flavoenzyme from Giardia places Giardiu close to the anaerobic bacteria in evolutionary terms.

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Section: Discussionmentioning

confidence: 51%

A H₂O‐Producing NADH Oxidase from the Protozoan Parasite Giardia Duodenalis

Brown

Upcroft

1996

European Journal of Biochemistry

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“…9,10 MTZ resistance is of clinical significance because it decreases the effectiveness of popular and affordable MTZ-containing anti-H. pylori therapies. 11,12 In addition, as MTZ is also used against a wide variety of prokaryotic and eukaryotic pathogens, [13][14][15] understanding the whole range of MTZ resistance mechanisms utilized by H. pylori may shed light on similar pathways in other clinically significant microbes.…”

Section: Introductionmentioning

confidence: 99%

Genetic analysis of Helicobacter pylori clinical isolates suggests resistance to metronidazole can occur without the loss of functional rdxA

Kim¹,

Joo²,

Lee³

et al. 2009

J Antibiot

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Resistance to metronidazole (MTZ) in Helicobacter pylori is associated with mutations in rdxA, encoding an oxygen-insensitive NADPH nitroreductase, and mutations in frxA, encoding a NAD(P)H-flavin oxidoreductase. Despite this association, the strict correlation of MTZ resistance with mutations in rdxA or frxA is still controversial. In this study, rdxA allelic replacement was used to distinguish resistance-associated nucleotide mutations from the natural genetic diversity of H. pylori. Replacement with truncated rdxA resulted in MTZ resistance, whereas replacement with missense-mutated rdxA from resistant clinical isolates failed to yield MTZ resistance. Thus, although truncation of rdxA confers MTZ resistance in G27 H. pylori, MTZ resistance found in other clinical isolates is not due to the identified amino-acid substitutions. Three of our MTZ-resistant clinical isolates expressed functional rdxA and two of these also encoded full-length frxA. Therefore, MTZ resistance can arise in H. pylori possessing functional rdxA, suggesting that other factors are involved in MTZ resistance.

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“…There is great intrinsic and public health interest in fully elucidating H. pylori's metabolic pathways and how H. pylori maintains its redox balance during microaerobic growth. Such knowledge should help us to understand the extraordinary chronicity of H. pylori infection and factors that determine whether a given infection will be benign or virulent, elucidate mechanisms of drug susceptibility and resistance, and identify potential targets for new effective antimicrobial agents.Here we focus on mechanisms of susceptibility and resistance of H. pylori to metronidazole (Mtz), a synthetic nitroimidazole that is a key component of popular and affordable anti-H. pylori therapies worldwide and that is also widely used against various anaerobic and parasitic infections (13,36,45). Resistance to Mtz is common among H. pylori strains, with frequencies among clinical isolates ranging from 10 to Ͼ90%, depending on geographic region and patient group (17,29,30).…”

mentioning

confidence: 99%

“…Here we focus on mechanisms of susceptibility and resistance of H. pylori to metronidazole (Mtz), a synthetic nitroimidazole that is a key component of popular and affordable anti-H. pylori therapies worldwide and that is also widely used against various anaerobic and parasitic infections (13,36,45). Resistance to Mtz is common among H. pylori strains, with frequencies among clinical isolates ranging from 10 to Ͼ90%, depending on geographic region and patient group (17,29,30).…”

mentioning

confidence: 99%

Sequential Inactivation of rdxA (HP0954) and frxA (HP0642) Nitroreductase Genes Causes Moderate and High-Level Metronidazole Resistance in Helicobacter pylori

et al. 2000

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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 g/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.Helicobacter pylori is a gram-negative microaerophilic bacterium that chronically infects human gastric epithelial cell surfaces and the overlying gastric mucin, a niche that few if any other microbes can occupy. It is carried by more than half of all people worldwide and is an important human pathogen: a major cause of peptic ulcer disease, and a contributor to other illnesses, ranging from childhood malnutrition to gastric cancer, and to increased susceptibility to other food-and waterborne pathogens (7,8,32,38,47). There is great intrinsic and public health interest in fully elucidating H. pylori's metabolic pathways and how H. pylori maintains its redox balance during microaerobic growth. Such knowledge should help us to understand the extraordinary chronicity of H. pylori infection and factors that determine whether a given infection will be benign or virulent, elucidate mechanisms of drug susceptibility and resistance, and identify potential targets for new effective antimicrobial agents.Here we focus on mechanisms of susceptibility and resistance of H. pylori to metronidazole (Mtz), a synthetic nitroimidazole that is a key component of popular and affordable anti-H. pylori therapies worldwide and that is also widely used against various anaerobic and parasitic infections (13,36,45). Resistance to Mtz is common among H. pylori strains, with frequencies among clinical isolates ranging from 10 ...

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Resistance to the nitroheterocyclic drugs

Cited by 84 publications

References 121 publications

A H₂O‐Producing NADH Oxidase from the Protozoan Parasite Giardia Duodenalis

A H₂O‐Producing NADH Oxidase from the Protozoan Parasite Giardia Duodenalis

Genetic analysis of Helicobacter pylori clinical isolates suggests resistance to metronidazole can occur without the loss of functional rdxA

Sequential Inactivation of rdxA (HP0954) and frxA (HP0642) Nitroreductase Genes Causes Moderate and High-Level Metronidazole Resistance in Helicobacter pylori

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Resistance to the nitroheterocyclic drugs

Cited by 84 publications

References 121 publications

A H2O‐Producing NADH Oxidase from the Protozoan Parasite Giardia Duodenalis

A H2O‐Producing NADH Oxidase from the Protozoan Parasite Giardia Duodenalis

Genetic analysis of Helicobacter pylori clinical isolates suggests resistance to metronidazole can occur without the loss of functional rdxA

Sequential Inactivation of rdxA (HP0954) and frxA (HP0642) Nitroreductase Genes Causes Moderate and High-Level Metronidazole Resistance in Helicobacter pylori

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A H₂O‐Producing NADH Oxidase from the Protozoan Parasite Giardia Duodenalis

A H₂O‐Producing NADH Oxidase from the Protozoan Parasite Giardia Duodenalis