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Transferable plasmid-mediated antibiotic resistance in Bacteroides
Abstract:
Plasmid-mediated resistance to chloramphenicol (Chlr), erythromycin (Eryr), tetracycline (Tetr) and clindamycin (Clindr) was transferred from three clinical isolates of Bacteroides fragilis and one faecal isolate of B. thetaiotaomicron to strains of B. fragilis, B. distasonis and Escherichia coli, and subsequently to B. fragilis and E. coli second-and third-stage recipients in series. Successful transfer was achieved by membrane-filter and centrifugation techniques that provide stable cell-to-cell contact but not by simple mixed broth culture. Chlr Eryr Tetr and Clindr Eryr were transferred at high frequency (1.9 x 10(-3)-1.8 x 10(-4)) but Tetr was transferred at low frequencies (1-1.6 x 10(-6)). Segregation of resistance markers was observed with selection for Tetr when donors were Chlr Eryr Tetr and Chlr Tetr. All transcipients were identical with the parent recipient strains but had the resistance markers of the donor strains. Resistance to antibiotics other than tetracycline was cured by growth with subinhibitory concentrations of aminoacridines and ethidium bromide for 24 h; cure of solitary Tetr required longer incubation (21 days). Identical plasmid DNA bands were demonstrated by agarose-gel electrophoresis in all the donor and corresponding transcipient strains but plasmids were not found in the recipient strains or in strains cured of resistance. Plasmid-mediated transferable antiobiotic resistance in Bacteroides spp. may compromise the treatment of infections and may provide a reservoir of antibiotic resistance in the intestinal flora.
Insights
Plasmid-mediated antibiotic resistance in Bacteroides species can spread to other bacteria. This transfer of resistance genes, particularly for chloramphenicol, erythromycin, and clindamycin, poses a significant threat to effective infection treatment.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Antibiotic resistance in anaerobic bacteria, particularly Bacteroides species, is a growing clinical concern.
- The role of plasmids in the dissemination of antibiotic resistance among Bacteroides and related gut bacteria is not fully understood.
Purpose of the Study:
- To investigate the transferability of plasmid-mediated antibiotic resistance genes between Bacteroides species and Escherichia coli.
- To characterize the frequency and stability of antibiotic resistance gene transfer mediated by plasmids.
Main Methods:
- Conjugative transfer experiments using membrane-filter and centrifugation techniques.
- Agarose-gel electrophoresis to identify plasmid DNA.
- Curing experiments using subinhibitory concentrations of aminoacridines and ethidium bromide.
Main Results:
- High-frequency transfer of chloramphenicol, erythromycin, and clindamycin resistance, but low-frequency transfer of tetracycline resistance.
- Successful plasmid-mediated transfer to B. fragilis, B. distasonis, and E. coli recipients.
- Segregation of resistance markers observed under specific selection pressures.
- Plasmid DNA confirmed in donor and transcipient strains, absent in recipients and cured strains.
Conclusions:
- Plasmid-mediated antibiotic resistance is readily transferable among Bacteroides and to E. coli.
- The transfer of these resistance genes can compromise antibiotic treatment efficacy.
- Bacteroides species act as a potential reservoir for antibiotic resistance genes within the intestinal flora.