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Molecular comparison of virulence plasmids in Shigella and enteroinvasive Escherichia coli
Abstract:
Virulent isolates of Shigella dysenteriae and Shigella boydii harboured a 140 Mdal plasmid which was either absent or deleted in spontaneously avirulent strains. Together with previous data concerning S. sonnei, S. flexneri and enteroinvasive Escherichia coli, the present results established the general role of extrachromosomal elements in the virulence of such enteroinvasive species. Among different species, these virulence plasmids showed unrelated endonuclease cleavage patterns, whereas hybridization experiments showed that homologous sequences were present throughout the molecules. These plasmids may therefore have derived from a common ancestor molecule which overcame evolutionary alterations in restriction sites. Furthermore, intraspecies and intraserotype comparison of these plasmids by endonuclease cleavage demonstrated highly conserved sequences. The consequences of these data for evolution, epidemiology and diagnosis of Shigella and enteroinvasive E. coli are discussed.
Insights
Virulent Shigella and E. coli strains often carry large plasmids essential for virulence. These virulence plasmids, though diverse, share common evolutionary origins and conserved sequences, impacting pathogen evolution and diagnosis.
Area of Science:
- Microbiology
- Genetics
- Molecular Biology
Background:
- Extrachromosomal elements, particularly plasmids, are implicated in the virulence of various bacterial pathogens.
- Previous studies suggested a role for plasmids in the virulence of Shigella sonnei, Shigella flexneri, and enteroinvasive Escherichia coli.
Purpose of the Study:
- To investigate the role of plasmids in the virulence of Shigella dysenteriae and Shigella boydii.
- To establish the general role of extrachromosomal elements in the virulence of enteroinvasive species.
Main Methods:
- Plasmid analysis using endonuclease cleavage patterns.
- Hybridization experiments to assess sequence homology between plasmids.
- Comparison of plasmid DNA from virulent and avirulent strains.
Main Results:
- A 140 Mdal plasmid was found in virulent Shigella dysenteriae and Shigella boydii, absent in avirulent strains.
- Virulence plasmids across different species showed distinct cleavage patterns but conserved homologous sequences.
- Intraspecies and intraserotype plasmid comparisons revealed highly conserved sequences.
Conclusions:
- Extrachromosomal elements play a general role in the virulence of Shigella and enteroinvasive E. coli.
- Virulence plasmids likely evolved from a common ancestor, undergoing alterations in restriction sites.
- Conserved plasmid sequences have implications for understanding bacterial evolution, epidemiology, and diagnostics.