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Characterization of plasmids from antibiotic-resistant Shigella isolates by agarose gell electrophoresis
Abstract:
Gel electrophoresis of DNA from 95 clinical isolates of Shigella sonnei and Shigella flexneri resistant to antibiotics revealed a heterogeneous plasmid population. Most of the plasmids were smaller than 6 megadaltons (Mdal). Six S. sonnei isolates with the most common antibiotic resistance pattern were characterized. They had two plasmids in common: one was a self-transmissible Fi+ plasmid of 46 Mdal encoding resistance to streptomycin and sulphafurazole. In addition, several cryptic plasmids ranging in size from 1.0 to 24.5 Mdal were present. Mobilization of the 5.5 Mdal SuSm plasmid and a 1.0 Mdal cryptic plasmid was demonstrated with all six S. sonnei isolates during conjugation. This mobilization was mediated by the 46 Mdal self-transmissible Fi+ R plasmid and also by a 24.5 Mdal Fi- plasmid carrying no known drug resistance determinants.
Insights
Antibiotic-resistant Shigella isolates harbor diverse plasmids, including a 46 Mdal self-transmissible plasmid conferring resistance. These plasmids can be mobilized by both the R plasmid and a cryptic plasmid, highlighting potential mechanisms for resistance gene spread.
Area of Science:
- Molecular Biology
- Microbiology
- Genetics
Background:
- Antibiotic resistance in bacterial pathogens is a significant public health concern.
- Shigella species, particularly Shigella sonnei and Shigella flexneri, are common causes of bacterial dysentery.
- Plasmids are known to play a crucial role in the dissemination of antibiotic resistance genes among bacteria.
Purpose of the Study:
- To characterize the plasmid profiles of antibiotic-resistant clinical isolates of Shigella sonnei and Shigella flexneri.
- To identify specific plasmids associated with common antibiotic resistance patterns.
- To investigate the mobilization capabilities of identified plasmids.
Main Methods:
- Gel electrophoresis was used to analyze the plasmid DNA from 95 clinical isolates.
- Six Shigella sonnei isolates with a prevalent antibiotic resistance pattern were further characterized.
- Conjugation experiments were performed to assess plasmid mobilization.
Main Results:
- A heterogeneous plasmid population was observed across the isolates, with most plasmids smaller than 6 megadaltons (Mdal).
- Six S. sonnei isolates shared a common plasmid profile including a 46 Mdal self-transmissible plasmid encoding resistance to streptomycin and sulphafurazole (SuSm), and various cryptic plasmids.
- Mobilization of a 5.5 Mdal SuSm plasmid and a 1.0 Mdal cryptic plasmid was demonstrated, mediated by the 46 Mdal R plasmid and a 24.5 Mdal Fi- plasmid.
Conclusions:
- The study identified a diverse range of plasmids in antibiotic-resistant Shigella isolates.
- A 46 Mdal self-transmissible plasmid is a key element in conferring streptomycin and sulphafurazole resistance.
- Plasmids, including cryptic ones, can be mobilized, suggesting potential mechanisms for the spread of antibiotic resistance determinants within Shigella populations.