R-factor mediated dihydrofolate reductases which confer trimethoprim resistance
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Abstract:
Six different R-factors conferring trimethoprim resistance had been isolated from a variety of sources. The trimethoprim-resistant dihydrofolate reductases (EC 1.5.1.3) from strains containing these R-factors were purified by ammonium sulphate precipitation and DEAE-cellulose ion-exchange chromatography. The enzymes showed no significant differences in molecular weight, pH profile, substrate profile, heat sensitivity, inhibition profile and Michaelis-Menten kinetics. There was, however, considerable variation in the specific activity of these enzymes in the same bacterial host. When two Escherichia coli trimethoprimsensitive dihydrofolate reductases were examined as controls, considerable differences between their properties and those of the enzymes mediated by R-factors were detected. The data suggest that one trimethoprim resistance gene could be spreading through the bacterial population, possibly situated on a transposon.
Insights
Six R-factors conferring trimethoprim resistance were studied. The resulting dihydrofolate reductase enzymes showed similar properties, suggesting a single resistance gene may be spreading via transposons.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Antibiotic resistance is a growing global health concern.
- R-factors are plasmids that confer resistance to antibiotics.
- Trimethoprim resistance is often mediated by dihydrofolate reductase (DHFR) enzymes.
Purpose of the Study:
- To investigate the biochemical properties of DHFR enzymes conferring trimethoprim resistance.
- To compare these enzymes with those from trimethoprim-sensitive bacteria.
- To explore the mechanism of trimethoprim resistance spread.
Main Methods:
- Isolation and purification of six different R-factors conferring trimethoprim resistance.
- Purification of trimethoprim-resistant DHFR enzymes using ammonium sulphate precipitation and DEAE-cellulose ion-exchange chromatography.
- Characterization of enzyme properties including molecular weight, pH profile, substrate profile, heat sensitivity, inhibition profile, and Michaelis-Menten kinetics.
Main Results:
- Purified DHFR enzymes from trimethoprim-resistant strains showed no significant differences in key biochemical properties.
- Considerable variation in specific activity was observed among these enzymes within the same bacterial host.
- DHFR enzymes from trimethoprim-sensitive Escherichia coli controls exhibited distinct properties compared to R-factor mediated enzymes.
Conclusions:
- The findings suggest that a single trimethoprim resistance gene may be disseminating within bacterial populations.
- This spread is potentially facilitated by mobile genetic elements like transposons.
- Further research is needed to confirm the role of transposons in the spread of trimethoprim resistance.