Pathogenicity islands (PAIs), as termed in 1990, are a distinct class of genomic islands acquired by microorganisms through horizontal gene transfer. Pathogenicity islands are found in both animal and plant pathogens. Although the general makeup of pathogenicity islands (PAIs) might vary throughout bacterial pathogen strains, all PAIs are known to have characteristics with all genomic islands, which includes virulence genes, functional mobility elements, and areas of homology to tRNA genes and direct repeats. Therefore, PAIs enables microorganisms to induce disease and also contribute to microorganisms' ability to evolve. The spread of antibiotic resistance and, more generally, the conversion of non-pathogenic strains in natural environments to strains that infect animal and plant hosts with disease are two examples of the evolutionary and ecological changes brought about by the transmission and acquisition of PAIs among bacterial species. An analogous genomic structure in rhizobia is termed a symbiosis island.
Properties
Pathogenicity islands (PAIs) are gene clusters incorporated in the genome, chromosomally or extrachromosomally, of pathogenic organisms, but are usually absent from those nonpathogenic organisms of the same or closely related species. They may be located on a bacterial chromosome or may be transferred within a plasmid or can be found in bacteriophage genomes. Bacteriophage integrases also found on pathogenicity islands (PAIs) are enzymes produced by bacteriophages to enable site-specific recombination between two recognition sequences, serving as another form of mobility element to enable PAIs insertion into host DNA.
- Yersinia pestis high pathogenicity island I has genes regulating iron uptake and storage.
- Salmonella SP-1 and SP-2 sites regulates bacterium's invasion and survival within host cells.
- Phage encoded Cholera toxin of Vibrio cholerae, Diphtheria toxin of Corynebacterium diphtheriae, Neurotoxins of Clostridium botulinum and Cytotoxin of Pseudomonas aeruginosa.