Pathogenicity Islands

Bacterial pathogens possess virulence factors that distinguish them from their non-pathogenic counterparts, and enable them to induce pathogenesis. Typically, these unique genes are encoded on specialized regions of the bacterial chromosome termed pathogenicity islands. Acquired through horizontal transmission, pathogenicity islands are large sections of the chromosome that differ in nucleotide content and in the presence of genetic elements compared to the core genome, and contain genes that promote pathogenesis. Pathogenicity islands were first discovered in bacteria belonging to the Enterobacteriaceae family, but are now known to exist in various animal and plant pathogens. As pathogenicity islands are unique to pathogenic bacteria, it is likely their presence permitted the emergence of bacterial pathogens and continues to shape their evolution. This chapter highlights the genetic organization and content of pathogenicity islands, their regulation, and their impact on the evolution of pathogenic bacteria.