A Tale about Shigella: Evolution, Plasmid, and Virulence.

Area of Science:

• Microbiology
• Bacterial Pathogenesis
• Molecular Biology

Background:

• Shigella species cause millions of intestinal infections annually, targeting the human colon mucosa.
• Shigella is a pathovar of Escherichia coli, distinguished by the pINV plasmid encoding virulence factors.
• It serves as a key model for studying intracellular bacterial pathogenesis.

Purpose of the Study:

• To review recent genetic advances in Shigella, focusing on its evolutionary history and pINV acquisition.
• To discuss insights into the maintenance mechanisms of the pINV plasmid.
• To describe the regulatory roles of transcription activators VirF, VirB, and MxiE in virulence gene expression.

Main Methods:

• Review of recent scientific literature on Shigella genetics and pathogenesis.
• Analysis of the evolutionary relationship between Shigella and Escherichia coli.
• Examination of the regulatory networks controlling virulence gene expression.

Main Results:

• Shigella's evolutionary path within the E. coli lineage is linked to pINV acquisition.
• Insights into the maintenance of the pINV plasmid are discussed.
• The roles of VirF, VirB, and MxiE in regulating type III secretion system and icsA expression are detailed.
• Interplay between pINV-encoded activators and chromosomal factors is highlighted.
• Novel MxiE-regulated chromosomal genes (icaR, icaT, yccT) are identified.

Conclusions:

• Shigella and E. coli share a history of balancing commensalism and pathogenesis.
• Understanding pINV regulation is crucial for deciphering Shigella virulence.
• The interplay between plasmid and chromosomal factors shapes Shigella pathogenesis.