Related Experiment Videos
Mechanisms of fluoroquinolone resistance: an update 1994-1998
1Division of Immunity and Infection, Medical School, University of Birmingham, Edgbaston, England. l.j.v.piddock@bham.ac.uk
Abstract:
Fluoroquinolone resistance is mediated by target changes (DNA gyrase and/or topoisomerase IV) and/or decreased intracellular accumulation. The genes (gyrA/gyrB/parC/parE) and proteins of DNA topoisomerase IV show great similarity, both at the nucleotide and amino acid sequence level to those of DNA gyrase. It has been shown that there are hotspots, called the quinolone resistance determining region (QRDR), for mutations within gyrA and parC. Based on the Escherichia coli co-ordinates, the hotspots most favoured for giving rise to decreased susceptibility and/or full resistance to quinolones are at serine 83 and aspartate 87 of gyrA, and at serine 79 and aspartate 83 for parC. Few mutations in gyrB or parE/grlB of any bacteria have been described. Efflux of fluoroquinolones is the major cause of decreased accumulation of these agents; for Staphylococcus aureus, the efflux pump involved in norfloxacin resistance is NorA, and for Streptococcus pneumoniae, PmrA. By analysis of minimum inhibitory concentration (MIC) data derived in the presence and absence of the efflux inhibitor reserpine, it has been shown that up to 50% of ciprofloxacin-resistant clinical isolates of S. pneumoniae may possess enhanced efflux. This suggests that efflux may be an important mechanism of clinical resistance in this species. In Pseudomonas aeruginosa, several efflux operons have been demonstrated genetically and biochemically. These operons are encoded by mex (Multiple EffluX) genes: mexAmexB-oprM, mexCD-OprJ system and mexEF-oprN system. The E. coli efflux pump is the acrAB-tolC system. Both the mar operon and the sox operon can give rise to multiple antibiotic resistance. It has been shown that mutations giving rise to increased expression of the transcriptional activators marA and soxS affect the expression of a variety of different genes, including ompF and acrAB. The net result is that expression of OmpF is reduced and much less drug is able to enter the cell; expression of acrAB is increased, enhancing efflux from the cell.
Insights
Fluoroquinolone resistance arises from target mutations or reduced drug accumulation via efflux pumps. Key resistance-determining regions in DNA gyrase and topoisomerase IV are identified, alongside bacterial efflux mechanisms like NorA and Mex systems.
Area of Science:
- Microbiology
- Molecular Biology
- Pharmacology
Background:
- Fluoroquinolone resistance is a growing clinical concern.
- Mechanisms include target modification and decreased intracellular drug accumulation.
- DNA gyrase and topoisomerase IV are primary fluoroquinolone targets.
Purpose of the Study:
- To elucidate the molecular mechanisms of fluoroquinolone resistance.
- To identify key genetic determinants of resistance.
- To understand the role of efflux pumps in fluoroquinolone resistance.
Main Methods:
- Analysis of quinolone resistance determining regions (QRDRs) in gyrA and parC genes.
- Investigation of efflux pump systems in various bacterial species (e.g., Staphylococcus aureus, Streptococcus pneumoniae, Pseudomonas aeruginosa, Escherichia coli).
- Use of efflux inhibitors (e.g., reserpine) to assess the contribution of efflux to resistance.
Main Results:
- Hotspots for mutations in gyrA (Ser83, Asp87) and parC (Ser79, Asp83) are crucial for resistance.
- Efflux pumps like NorA (S. aureus) and PmrA (S. pneumoniae) significantly contribute to fluoroquinolone resistance.
- Multiple efflux operons (e.g., mex, acrAB-tolC) and regulatory systems (mar, sox) are involved in resistance in Gram-negative bacteria.
Conclusions:
- Fluoroquinolone resistance is multifactorial, involving target mutations and enhanced efflux.
- Understanding these mechanisms is vital for developing strategies to combat resistance.
- Efflux pumps represent significant targets for overcoming fluoroquinolone resistance in clinical settings.