Pathogenicity Islands: Properties and Types

 Pathogenicity islands (PAIs) are large groups of mobile genetic elements that are associated with pathogenicity and are located on the bacterial chromosome. These genetic elements are thought to have evolved from lysogenic bacteriophages and plasmids and are transferred by horizontal gene transfer. The concept of PAI was founded in the late 1980s by Jörg Hacker and colleagues.

PAIs are typically comprised of one or more virulence-associated genes and “mobility” genes (i.e., integrases and transposases) that mediate movements between various genetic elements (e.g., plasmids, and chromosomes) and among different bacterial strains.

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. Pathogenicity islands have one or more virulence genes
  2. PAIs are large organized groups of genes, usually 100 to 200 kb in size.
  3. They are found with parts of the genome associated with mobile genetic elements and cause genetic instability
  4. These islands 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 are:

Genus/SpeciesPAI NameVirulence Characteristics
Escherichia  coliPAI I536Alpha hemolysin, fimbriae, adhesions, in urinary tract infections.
Escherichia coliPAI Ij96Alpha hemolysin, P-pilus in urinary tract infections
Escherichia coli (EHEC)01#7Macrophage toxin of enterohaemorrhagic Escherichia coli
Salmonella typhimuriumSPI-1Invasion and damage of host cells, diarrhea
Yersinia pestisHPI/pgmGene that enhance iron uptake
Vibrio cholerae EL tor O1VPI-1Neuraminidase, utilization of amino sugars
Staphylococcus aureusSCC mecMethicillin and other antibiotic resistance
Staphylococcus aureusSaPI1Toxic shock syndrome toxin-1, enterotoxin
Enterococcus faecalisNPmCytolysin, biofilm formation

 Source: LANGE Medical Microbiology/PubMed Central

Acharya Tankeshwar

Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. As an asst. professor, I am teaching microbiology and immunology to medical and nursing students at PAHS, Nepal. I have been working as a microbiologist at Patan hospital for more than 10 years.

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