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Molecular mechanisms of resistance to trimethoprim
Abstract:
Resistance to inhibitors of dihydrofolate reductase arises from a variety of mechanisms involving enzyme alteration, cellular impermeability, enzyme overproduction, inhibitor modification, and loss of binding capacity. The mechanism of greatest clinical importance is the production of plasmid-encoded, trimethoprim-resistant forms of dihydrofolate reductase. At least two different types of these enzymes have been documented. The trimethoprim-resistant reductases differ from all other dihydrofolate reductases in molecular weight, subunit structure, kinetic properties, and binding of inhibitors. Colony hybridization techniques, developed for the detection of plasmid DNA coding for trimethoprim-resistant reductases, enable researchers to evaluate the prevalence and distribution of plasmid-borne resistance. Preliminary results obtained with a series of enzymatically characterized clinical isolates suggest that the colony hybridization technique may provide a convenient epidemiological tool for monitoring the dissemination of plasmid-borne resistance to trimethoprim.
Insights
Dihydrofolate reductase inhibitors face resistance primarily through plasmid-encoded enzymes. Colony hybridization offers a new tool to track the spread of this trimethoprim resistance.
Area of Science:
- Biochemistry
- Molecular Biology
- Microbiology
Background:
- Dihydrofolate reductase (DHFR) inhibitors are crucial antimicrobials.
- Resistance mechanisms include enzyme alteration, reduced permeability, and overproduction.
- Plasmid-encoded DHFR variants are clinically significant resistance factors.
Purpose of the Study:
- To investigate the molecular basis of DHFR inhibitor resistance.
- To characterize novel trimethoprim-resistant DHFR enzymes.
- To evaluate colony hybridization for detecting plasmid-borne resistance.
Main Methods:
- Enzymatic characterization of clinical isolates.
- Molecular analysis of DHFR variants.
- Colony hybridization assays for plasmid DNA detection.
Main Results:
- Identified at least two distinct plasmid-encoded trimethoprim-resistant DHFR types.
- These resistant enzymes exhibit unique molecular weights, structures, and kinetic properties.
- Colony hybridization effectively detected plasmid DNA encoding resistant DHFR.
Conclusions:
- Plasmid-mediated DHFR alteration is a key resistance mechanism.
- Trimethoprim-resistant DHFR enzymes possess distinct biochemical profiles.
- Colony hybridization is a promising epidemiological tool for monitoring resistance dissemination.