Pathogenicity islands (PAIs) of Human Pathogen: Properties and Types

 Pathogenicity islands (PAIs) are large group of mobile genetic elements that are associated with pathogenicity and are located on the bacterial chromosome. The concept of PAI was founded in the late 1980s by Jörg Hacker and colleagues.
The presence of pathogenicity islands (PAIs) in the genomes of bacterial pathogens is one of the main features that differentiate them from closely related nonpathogenic strains or species.
The major properties of PAIs are as follows:
1.       PAIs have one or more virulence genes;
2.       PAIs are present in the genome of the pathogenic member of a species, but absent in the nonpathogenic members;
3.       PAIs are large organized group of genes, usually 100 to 200 kb in size.
4.       PAIs are found with parts of the genome associated .with mobile genetic elements;
5.       PAIs often have genetic instability
6.       PAIs typically have different guanine plus cytosine content than the rest of the bacterial genome.
Few examples of the very large number of pathogenicity islands of human pathogens
PAI Name
Virulence Characteristics
Escherichia  coli
PAI I536
Alpha hemolysin, fimbriae, adhesions, in urinary tract infections.
Escherichia coli
PAI Ij96
Alpha hemolysin, P-pilus in urinary tract infections
Macrophage toxin of enterohaemorrhagic Escherichia coli
Salmonella typhimurium
Invasion and damage of host cells, diarrhea
Yersinia pestis
Gene that enhance iron uptake
Vibrio cholerae EL tor O1
Neuraminidase, utilization of amino sugars
Staphylococcus aureus
SCC mec
Methicillin and other antibiotic resistance
Staphylococcus aureus
Toxic shock syndrome toxin-1, enterotoxin
Enterococcus faecalis
Cytolysin, biofilm formation
Source: LANGE Medical Microbiology/PubMed Central