New insights about excisable pathogenicity islands in Salmonella and their contribution to virulence.

Pathogenicity islands (PAIs) are regions of the chromosome of pathogenic bacteria that harbor virulence genes, which were probably acquired by lateral gene transfer. Several PAIs can excise from the bacterial chromosome by site-specific recombination and in this review have been denominated "excisable PAIs". Here, the characteristic of some of the excisable PAIs from Salmonella enterica and the possible role and impact of the excision process on bacterial virulence is discussed. Understanding the role of PAI excision could provide important insights relative to the emergence, evolution and virulence of pathogenic enterobacteria.