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Conjugal transfer of imipenem resistance in Bacteroides fragilis
1Institute of Anaerobic Bacteriology, Gifu University School of Medicine, Japan.
Abstract:
Transfer of imipenem resistance in Bacteroides fragilis was studied. Clinical isolate B. fragilis 10-73 was highly resistant to imipenem. Imipenem resistance was transferred from 10-73 to B. fragilis strain TM4000 at a frequency of 10(-6)/input recipient by a filter mating technique. The resistance could also be retransferred. B. fragilis 10-73 and both primary and secondary transcipients produced an imipenem-hydrolyzing metallo-beta-lactamase. Acquisition of imipenem resistance correlated with the appearance of plasmid DNA with a size (ca. 13.6 kb) similar to that of the donor strain. TM4000 transformed by electroporation with purified DNA of the 13.6-kb plasmid pBFUK1 produced the metallo-beta-lactamase and was resistant to imipenem. Transfer was resistant to DNase treatment and no transfer was seen with a sterile filtrate of the donor culture. It is suggested that gene transfer in B. fragilis has the properties of a conjugation system rather than those of transformation or transduction.
Insights
Imipenem resistance transfer in Bacteroides fragilis was studied. A 13.6-kb plasmid mediated this transfer, suggesting a conjugation system for imipenem resistance gene spread.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Imipenem is a critical antibiotic for treating serious infections.
- Carbapenem resistance, particularly in anaerobic bacteria like Bacteroides fragilis, poses a significant clinical challenge.
- Understanding resistance mechanisms and transfer is crucial for effective antimicrobial stewardship.
Purpose of the Study:
- To investigate the mechanism and transfer of imipenem resistance in a clinical isolate of Bacteroides fragilis.
- To identify the genetic element responsible for imipenem resistance.
- To characterize the mode of gene transfer.
Main Methods:
- Filter mating technique for bacterial conjugation experiments.
- Plasmid DNA isolation and characterization.
- Electroporation for bacterial transformation.
- Detection of metallo-beta-lactamase activity.
Main Results:
- Imipenem resistance was successfully transferred from a clinical isolate (B. fragilis 10-73) to a recipient strain (TM4000) at a frequency of 10(-6).
- The transfer was mediated by a ~13.6 kb plasmid (pBFUK1) and associated with the production of an imipenem-hydrolyzing metallo-beta-lactamase.
- Resistance transfer exhibited characteristics of conjugation, being DNase-resistant and not occurring via sterile filtrate.
Conclusions:
- A novel plasmid-mediated imipenem resistance mechanism involving a metallo-beta-lactamase was identified in Bacteroides fragilis.
- The findings suggest that conjugation is the primary mechanism for the spread of this imipenem resistance gene within B. fragilis populations.
- This study highlights the potential for rapid dissemination of antibiotic resistance in clinically important anaerobic bacteria.