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Composition, acquisition, and distribution of the Vi exopolysaccharide-encoding Salmonella enterica pathogenicity

Derek Pickard1, John Wain, Stephen Baker

  • 1Centre for Molecular Microbiology and Infection, Department of Biological Sciences, Imperial College of Science, Technology and Medicine, Armstrong Road, London SW7 2AZ, UK. d.pickard@imperial.ac.uk

Journal of Bacteriology
|August 19, 2003
PubMed

Insights

The Salmonella enterica serovar Typhi pathogenicity island SPI-7, encoding Vi capsular polysaccharide, shows structural similarities across serovars Typhi, Paratyphi C, and Dublin. This mobile genetic element may have evolved through multiple insertions.

Area of Science:

  • Microbiology
  • Genetics
  • Genomics

Background:

  • The viaB locus, responsible for Vi capsular polysaccharide production in Salmonella enterica, is not universally distributed among serovars.
  • In Salmonella enterica serovar Typhi, the viaB locus resides on a large pathogenicity island, SPI-7, situated between duplicated tRNA(pheU) sites.

Purpose of the Study:

  • To investigate the structure and distribution of the SPI-7 pathogenicity island in different Salmonella enterica serovars.
  • To understand the evolutionary origins and potential mobility of the SPI-7 island.

Main Methods:

  • Functional and bioinformatic analysis of the SPI-7 island.
  • Comparative DNA sequence analysis of SPI-7 in Salmonella enterica serovars Typhi, Paratyphi C, and Dublin.
  • Examination of 30 additional Salmonella serovars for insertions at the tRNA(pheU) site.

Main Results:

  • SPI-7 islands in serovars Typhi, Paratyphi C, and Dublin share over 99% DNA sequence identity, with variations in specific gene content (e.g., SopE bacteriophage, type IV pilus).
  • Most other Salmonella serovars examined lacked insertions at the equivalent tRNA(pheU) site, indicating limited distribution of SPI-7.
  • Sequence analysis suggests SPI-7 may function as a mobile genetic element, potentially a conjugative transposon or integrated plasmid remnant, with homologous gene clusters found in other bacteria.

Conclusions:

  • The SPI-7 pathogenicity island is conserved across key Salmonella serovars but exhibits variations, suggesting adaptation and evolution.
  • The mosaic structure and sequence homology with other bacterial gene clusters support the hypothesis that SPI-7 is a mobile element.
  • Understanding SPI-7's structure and mobility provides insights into Salmonella pathogenesis and evolution.

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