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.

Figure: Genetic Structure of PAI

 

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

Genus/Species	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
Escherichia coli (EHEC)	01#7	Macrophage toxin of enterohaemorrhagic Escherichia coli
Salmonella typhimurium	SPI-1	Invasion and damage of host cells, diarrhea
Yersinia pestis	HPI/pgm	Gene that enhance iron uptake
Vibrio cholerae EL tor O1	VPI-1	Neuraminidase, utilization of amino sugars
Staphylococcus aureus	SCC mec	Methicillin and other antibiotic resistance
Staphylococcus aureus	SaPI1	Toxic shock syndrome toxin-1, enterotoxin
Enterococcus faecalis	NPm	Cytolysin, biofilm formation

                
Source: LANGE Medical Microbiology/PubMed Central