
Full text loading...
Category: Microbial Genetics and Molecular Biology
The Virulence Plasmid of Shigellae: an Archipelago of Pathogenicity Islands?, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555818173/9781555811617_Chap08-1.gif /docserver/preview/fulltext/10.1128/9781555818173/9781555811617_Chap08-2.gifAbstract:
Shigella strains are gram-negative, nonsporulating, nonencapsulated, facultative aerobic, nonmotile, straight rods that belong to the family Enterobacteriaceae and to the tribe Escherichiaeae. These observations suggest that virulence plasmids are made up of conserved building blocks and that some differences between various plasmids might be the result of shuffling of these building blocks. This chapter focuses on genes carried by the virulence plasmid that are or might be involved in the pathogenicity of Shigella. The virulence plasmid is an IncFII replicon, and functions involved in plasmid maintenance and stability have been recently described. Three genes carried by the virulence plasmid have been implicated in the ability of Shigella to move within the cytoplasm of infected cells: icsA (virG), sopA (icsP),and virK. The current model proposes that binding of H-NS to the virB promoter at low temperature prevents its activation by VirF. SepA homologs such as PssA from Shiga toxin-producing E. coli and EspP from enterohemorrhagic E. coli are also encoded by virulence plasmids and are flanked by sequences related to IS600,IS911,IS203, and IS7. Two different genes, designated apy and phoN-Sf, encoding periplasmic phosphatases about 25 kDa have been cloned from the virulence plasmid of two S. flexneri isolates of serotype 2a. So far, all the proteins identified as or proposed to be effectors of the specific interactions that occur between Shigella and host cells are encoded by the virulence plasmid.
Full text loading...
Genetic organization of the entry region. The 31-kb entry region of the Shigella virulence plasmid is shown in a discontinuous manner, and the gene order reads from top to bottom and from left to right. Shigella genes are shown by open arrows (not to scale), and their names are indicated in bold type. Numbers indicate the size (in base pairs) of intergenic regions. Homologous genes present in the SPI-1 region at centisome 68 of the Salmonella chromosome (see references 33 and 56 for reviews) are indicated in standard characters below the Shigella genes; gene clusters are indicated by thin arrows.
Genetic organization of the entry region. The 31-kb entry region of the Shigella virulence plasmid is shown in a discontinuous manner, and the gene order reads from top to bottom and from left to right. Shigella genes are shown by open arrows (not to scale), and their names are indicated in bold type. Numbers indicate the size (in base pairs) of intergenic regions. Homologous genes present in the SPI-1 region at centisome 68 of the Salmonella chromosome (see references 33 and 56 for reviews) are indicated in standard characters below the Shigella genes; gene clusters are indicated by thin arrows.
Schematic genetic map of pWR100, the virulence plasmid of S. flexneri M90T. The virulence plasmid is shown in a circular form, on which the position of genes is indicated by thick lines and their direction of transcription is indicated by arrows. The positions of virF, ipaH1.4, ipaH2.5, phoN,and senA have not been determined. Numbers refer to the coordinates on the plasmid, in kilobases.
Schematic genetic map of pWR100, the virulence plasmid of S. flexneri M90T. The virulence plasmid is shown in a circular form, on which the position of genes is indicated by thick lines and their direction of transcription is indicated by arrows. The positions of virF, ipaH1.4, ipaH2.5, phoN,and senA have not been determined. Numbers refer to the coordinates on the plasmid, in kilobases.