The roles of two-component systems in virulence of pathogenic Escherichia coli and Shigella spp.

Two-component systems (TCSs) are well conserved among E. coli strains, including pathogenic E. coli and also closely related Shigella spp. Although 25% of the genome of pathogenic E. coli is strain-specific, only small number of strain-specific TCSs is found. Regulation of virulence genes in response to environmental stimuli is partly dependent on TCSs commonly present in nonpathogenic E. coli strains. Some virulence genes are directly regulated by response regulator ofTCS but some are affected at posttranscriptional steps of production or assembly ofmacromolecule by TCS-induced products. In the process ofacquiringvirulence traits, regulatory systems for virulence genes expression seem to be built by integrating E. coli backbone TCSs with the virulence regulatory network via transcription regulatory gene.