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Mutator plasmid in a nalidixic acid-resistant strain of Shigella dysenteriae type 1
J E Ambler1, Y J Drabu, P H Blakemore
1Department of Pharmaceutics, School of Pharmacy, University of London, UK.
Abstract:
A clinical isolate of Shigella dysenteriae from Kashmir, resistant to seven antibacterial agents including nalidixic acid, carried four plasmids, only one of which was transferable by conjugation. This plasmid, designated pYD1, conferred trimethoprim resistance and increased the frequency of mutation to nalidixic acid resistance in recipient strains. Thus, although nalidixic acid resistance was not carried on a transferable plasmid, the presence of pYD1 increased the frequency at which the strain mutated to nalidixic acid resistance.
Insights
A Shigella dysenteriae clinical isolate showed high antibacterial resistance. A transferable plasmid, pYD1, conferred trimethoprim resistance and increased nalidixic acid resistance mutation frequency in recipient strains.
Area of Science:
- Microbiology
- Genetics
- Infectious Diseases
Background:
- Shigella dysenteriae is a significant cause of bacterial dysentery.
- Antibiotic resistance in bacterial pathogens is a growing global health concern.
- Plasmids are key vehicles for the dissemination of antimicrobial resistance genes.
Purpose of the Study:
- To characterize the plasmids of an antibiotic-resistant Shigella dysenteriae clinical isolate.
- To investigate the role of transferable plasmids in conferring antimicrobial resistance.
- To determine the mechanism by which nalidixic acid resistance arises in this isolate.
Main Methods:
- Plasmid DNA extraction and characterization from a clinical isolate.
- Conjugation experiments to assess plasmid transferability.
- Antimicrobial susceptibility testing of recipient strains.
- Mutation frequency analysis for nalidixic acid resistance.
Main Results:
- The isolate harbored four plasmids; only one, pYD1, was transferable.
- Plasmid pYD1 conferred resistance to trimethoprim.
- The presence of pYD1 significantly increased the mutation frequency to nalidixic acid resistance in recipient strains.
- Nalidixic acid resistance itself was not located on the transferable plasmid.
Conclusions:
- A transferable plasmid (pYD1) in Shigella dysenteriae mediates trimethoprim resistance.
- This plasmid enhances the spontaneous mutation rate towards nalidixic acid resistance, even though the resistance gene is not plasmid-borne.
- Understanding plasmid-mediated resistance mechanisms is crucial for combating infectious diseases.