Composition, acquisition, and distribution of the Vi exopolysaccharide-encoding Salmonella enterica pathogenicity island SPI-7

Derek Pickard, John Wain, Stephen Baker, Alexandra Line, Sonia Chohan, Maria Fookes, Andrew Barron, Peadar O Gaora, José A. Chabalgoity, Niren Thanky, Christoph Scholes, Nicholas Thomson, Michael Quail, Julian Parkhill, Gordon Dougan

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124 Citations (Scopus)


Vi capsular polysaccharide production is encoded by the viaB locus, which has a limited distribution in Salmonella enterica serovars. In S. enterica serovar Typhi, viaB is encoded on a 134-kb pathogenicity island known as SPI-7 that is located between partially duplicated tRNApheU sites. Functional and bioinformatic analysis suggests that SPI-7 has a mosaic structure and may have evolved as a consequence of several independent insertion events. Analysis of viaB-associated DNA in Vi-positive S. enterica serovar Paratyphi C and S. enterica serovar Dublin isolates revealed the presence of similar SPI-7 islands. In S. enterica serovars Paratyphi C and Dublin, the SopE bacteriophage and a 15-kb fragment adjacent to the intact tRNApheU site were absent. In S. enterica serovar Paratyphi C only, a region encoding a type IV pilus involved in the adherence of S. enterica serovar Typhi to host cells was missing. The remainder of the SPI-7 islands investigated exhibited over 99% DNA sequence identity in the three serovars. Of 30 other Salmonella serovars examined, 24 contained no insertions at the equivalent tRNApheU site, 2 had a 3.7-kb insertion, and 4 showed sequence variation at the tRNApheU-phoN junction, which was not analyzed further. Sequence analysis of the SPI-7 region from S. enterica serovar Typhi strain CT18 revealed significant synteny with clusters of genes from a variety of saprophytic bacteria and phytobacteria, including Pseudomonas aeruginosa and Xanthomonas axonopodis pv. citri. This analysis suggested that SPI-7 may be a mobile element, such as a conjugative transposon or an integrated plasmid remnant.
Original languageEnglish
Pages (from-to)5055-5065
Number of pages11
JournalJournal of Bacteriology
Issue number17
Publication statusPublished - Sep 2003

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