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Plasmid analysis of clinical isolates of Bacteroides fragilis group strains
1Department of Clinical Microbiology, Albert Szent Györgyi University Medical School, Szeged, Hungary.
Abstract:
Cryptic plasmids were isolated from 26 of 52 Bacteroides fragilis group strains derived from severe infections. Four strains harboured two plasmids, one three plasmids and one five plasmids with different molecular weights. The same molecular weight plasmid (3.7 Md) was isolated from 17 of the 26 plasmid-containing B. fragilis group strains. No correlation was found between plasmid-harbouring and resistance against ten antibiotics and different heavy metal ions. No curing of the strains from the plasmids was achieved with ethidium bromide and acridine orange.
Insights
Cryptic plasmids were found in half of Bacteroides fragilis strains from severe infections. A common 3.7 Md plasmid was prevalent, but not linked to antibiotic or heavy metal resistance.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Bacteroides fragilis group strains are significant human gut commensals and opportunistic pathogens.
- Cryptic plasmids are extrachromosomal DNA elements found in bacteria, often without a known function.
- Understanding plasmid presence and characteristics in pathogenic bacteria is crucial for infection control.
Purpose of the Study:
- To investigate the presence and characteristics of cryptic plasmids in Bacteroides fragilis group strains isolated from severe human infections.
- To determine if specific plasmids correlate with antibiotic or heavy metal resistance.
- To assess the efficacy of common curing agents on these plasmids.
Main Methods:
- Isolation and characterization of plasmids from 52 Bacteroides fragilis group strains.
- Plasmid molecular weight determination.
- Testing for antibiotic and heavy metal resistance.
- Attempting plasmid curing using ethidium bromide and acridine orange.
Main Results:
- Cryptic plasmids were detected in 26 of 52 (50%) strains.
- A 3.7 Md plasmid was the most common, found in 17 of the 26 plasmid-positive strains.
- No correlation was observed between plasmid carriage and resistance to ten antibiotics or heavy metal ions.
- Ethidium bromide and acridine orange failed to cure the plasmids.
Conclusions:
- Cryptic plasmids are common in Bacteroides fragilis group strains associated with severe infections.
- The prevalent 3.7 Md plasmid does not appear to confer resistance to common antibiotics or heavy metals in this context.
- Standard plasmid curing methods were ineffective, suggesting unique plasmid biology or stable integration.