Mechanism of action of and resistance to quinolones (original) (raw)
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Mechanism of plasmid-mediated quinolone resistance
Proceedings of The National Academy of Sciences, 2002
Quinolones are potent antibacterial agents that specifically target bacterial DNA gyrase and topoisomerase IV. Widespread use of these agents has contributed to the rise of bacterial quinolone resistance. Previous studies have shown that quinolone resistance arises by mutations in chromosomal genes. Recently, a multiresistance plasmid was discovered that encodes transferable resistance to quinolones. We have cloned the plasmid-quinolone resistance gene, termed qnr, and found it in an integron-like environment upstream from qacE⌬1 and sulI. The gene product Qnr was a 218-aa protein belonging to the pentapeptide repeat family and shared sequence homology with the immunity protein McbG, which is thought to protect DNA gyrase from the action of microcin B17. Qnr had pentapeptide repeat domains of 11 and 28 tandem copies, separated by a single glycine with a consensus sequence of A͞C D͞N L͞F X X. Because the primary target of quinolones is DNA gyrase in Gram-negative strains, we tested the ability of Qnr to reverse the inhibition of gyrase activity by quinolones. Purified Qnr-His6 protected Escherichia coli DNA gyrase from inhibition by ciprofloxacin. Gyrase protection was proportional to the concentration of Qnr-His6 and inversely proportional to the concentration of ciprofloxacin. The protective activity of Qnr-His6 was lost by boiling the protein and involved neither quinolone inactivation nor independent gyrase activity. Protection of topoisomerase IV, a secondary target of quinolone action in E. coli, was not evident. How Qnr protects DNA gyrase and the prevalence of this resistance mechanism in clinical isolates remains to be determined.
2003
Quinolones are broad-spectrum antibacterial agents, commonly used in both clinical and veterinary medicine. Their extensive use has resulted in bacteria rapidly developing resistance to these agents. Two mechanisms of quinolone resistance have been established to date: alter- ations in the targets of quinolones, and decreased accumulation due to impermeability of the membrane and/or an overexpression of efflux pump systems. Recently,
Quinolones: Action and Resistance Updated
Current Topics in Medicinal Chemistry, 2009
The quinolones trap DNA gyrase and DNA topoisomerase IV on DNA as complexes in which the DNA is broken but constrained by protein. Early studies suggested that drug binding occurs largely along helix-4 of the GyrA (gyrase) and ParC (topoisomerase IV) proteins. However, recent X-ray crystallography shows drug intercalating between the -1 and +1 nucleotides of cut DNA, with only one end of the drug extending to helix-4. These two models may reflect distinct structural steps in complex formation. A consequence of drug-enzyme-DNA complex formation is reversible inhibition of DNA replication; cell death arises from subsequent events in which bacterial chromosomes are fragmented through two poorly understood pathways. In one pathway, chromosome fragmentation stimulates excessive accumulation of highly toxic reactive oxygen species that are responsible for cell death. Quinolone resistance arises stepwise through selective amplification of mutants when drug concentrations are above the MIC and below the MPC, as observed with static agar plate assays, dynamic in vitro systems, and experimental infection of rabbits. The gap between MIC and MPC can be narrowed by compound design that should restrict the emergence of resistance. Resistance is likely to become increasingly important, since three types of plasmid-borne resistance have been reported.
Mechanisms of quinolone resistance
Infection, 1994
Two mechanisms of resistance to fluoroquinolones are known: (i) alteration of the molecular target of quinolone action-DNA gyrase, and (ii) reduction of the quinolone accumulation. Mutations altering the N-terminus of the gyrase A subunit, especially those around residues Ser83 and Asp87, significantly reduce the susceptibilities towards all quinolones, while alterations of the gyrase B subunit are rarely found and are of minor importance. Reduced drug accumulation is associated with alterations of the outer membrane protein profile in gram-negative bacteria. Such mutations include the marA locus in Escherichia coli and result in low level resistance towards quinolones and unrelated drugs.
Interaction of the Plasmid-Encoded Quinolone Resistance Protein Qnr with Escherichia coli DNA Gyrase
Antimicrobial Agents and Chemotherapy, 2005
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Alterations in the DNA topoisomerase IV grlA gene responsible for quinolone resistance in
Antimicrobial Agents and Chemotherapy
A 4.2-kb DNA fragment conferring quinolone resistance was cloned from a quinolone-resistant clinical isolate of Staphylococcus aureus and was shown to possess a part of the grlB gene and a mutated grlA gene. S-803F and E-843K mutations in the grlA gene product were responsible for the quinolone resistance. The mutated grlA genes responsible for quinolone resistance were dominant over the wild-type allele, irrespective of gene dosage in a transformation experiment with the grlA gene alone. However, dominance by mutated grlA genes depended on gene dosage when bacteria were transformed with the grlA and grlB genes in combination. Quinolone-resistant gyrA mutants were easily isolated from a strain, S. aureus RN4220, carrying a plasmid with the mutated grlA gene, though this was not the case for other S. aureus strains lacking the plasmid. The elimination of this plasmid from such quinolone-resistant gyrA mutants resulted in marked increases in quinolone susceptibility. These results suggest that both DNA gyrase and DNA topoisomerase IV may be targets of quinolones and that the quinolone susceptibility of organisms may be determined by which of these enzymes is most quinolone sensitive. , norfloxacin (15), and ciprofloxacin (5) were synthesized at Discovery Research Laboratories II, Dainippon Pharmaceutical Co., Ltd. Ampicillin, chloramphenicol, kanamycin, and novobiocin were purchased from Sigma Chemical Co. (St. Louis, Mo.). Other compounds were purchased from Nacalai Tesque (Kyoto, Japan) unless otherwise indicated.
Resistance to Quinolones in Gram-Negative Microorganisms: Mechanisms and Prevention
European Urology
Bacterial resistance to quinolones is essentially the result of mutations on several genes involved in the synthesis of DNA-gyrase or in proteins of the cellular envelope. A single mutational event may lead to complete resistance to older quinolones, but clinical resistance to newer quinolones such as norfloxacin requires two or more mutations. Prevention of resistance to norfloxacin requires prevention of the strains carrying 'first mutations' (by a controlled use of older quinolones) and the early detection of such strains. If microbiologie and pharmacologic data are taken into account at the same time, the incidence of norfloxacin-resistant strains in urinary tract infections will remain insignificant. coli Kl 2. In these experiments the strain is heavily inoc ulated on culture media containing different quinolone concentrations, and the survivors (presumptively mu tants) are studied and further characterized. The opera tive designation of mutants is arbitrarily chosen by each author. Thus, mutants selected on norfloxacin have been designated as nfx or nor, those selected on ciprofloxacin as cfx, and those selected on nalidixic acid as nal. These designations do not imply any relationship with the accepted designations of the bacterial genes [1], For instance, the nalA mutation has been localized inside the gene gyrA-as have nfxZ, norA and cfxA-and must be considered as gyrA mutations. Whether they are the same or different mutations inside the gene will be ascer tained by precise genetic studies and, finally, by DNA sequencing. Although mutations on the same gene tend to produce similar or identical phenotypes, this is not always the case. The modified regions of the gene may have differ ent functional consequences in the resulting polypeptide, leading, for instance, to different levels of quinolone resistance. In order to prevent confusion about the dif ferent published designations of the mutants resistant to quinolones, table 1 summarizes the different mutations in relation to the presumed bacterial gene involved.
Interaction of plasmid and host quinolone resistance
Journal of Antimicrobial Chemotherapy, 2003
Sir, Resistance to quinolones in Gram-negative bacteria is usually caused by chromosomal mutations that alter the target enzymes DNA gyrase and topoisomerase IV or activate the efflux systems that pump the drugs out of the cytoplasm. Loss of porin channels for drug entry may also contribute to resistance, but is less important. Plasmid-mediated quinolone resistance, long thought not to exist, has recently been discovered. 1 Conjugative plasmid pMG252, found in a clinical isolate of Klebsiella pneumoniae, mediates a four-to 16-fold increase in resistance to fluoroquinolones and nalidixic acid, thus facilitating ciprofloxacin MICs as high as 32 mg/L in a K. pneumoniae strain already partially quinolone resistant. In wild-type K. pneumoniae or Escherichia coli strains pMG252 still augmented resistance but only to ciprofloxacin MICs of 0.125-0.25 mg/L, well below the clinical breakpoint for loss of susceptibility. However, from such an E. coli strain carrying pMG252, mutants could be selected with successively higher levels of resistance up to a ciprofloxacin MIC of 4 mg/L. 1 The plasmid locus responsible for quinolone resistance is termed qnr. The gene has been cloned and sequenced. It encodes a 218-amino-acid protein that belongs to the pentapeptide repeat family of proteins. 2 Purified Qnr has been shown to block inhibition of E. coli DNA gyrase by ciprofloxacin in a cell-free system. 2 The objective of the present study was to evaluate the interaction of resistance determined by plasmid pMG252 with defined chromosomal mechanisms of quinolone resistance to gain an insight into how higher levels of resistance could develop.
European Journal of Clinical Microbiology & Infectious Diseases, 2002
The quinolones are a potent class of antimicrobial agents that target two essential enzymes of bacterial cells: DNA gyrase and topoisomerase IV. Resistance is mediated chiefly through stepwise mutations in the genes that encode these enzymes, leading to alterations of the target site. These mutations occur in an area called the "quinolone resistance determining region". In gram-positive organisms, mutations occur more often in topoisomerase IV than in DNA gyrase. This target preference appears to depend upon two factors: the species of organism and the selecting drug. Resistance can be enhanced by a decrease in intracellular drug concentration, which is mediated through efflux pumps. The newer generation of fluoroquinolones and non-fluorinated quinolones exhibits enhanced activity against gram-positive organisms compared to the older members of this drug class, although development of resistance to these drugs has been demonstrated in vitro. This review gives a chronological perspective of the literature on the action of DNA gyrase and topoisomerase IV and the mechanisms of resistance to quinolones in staphylococci, streptococci and enterococci.