Pathogenicity island

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (September 2011)

Pathogenicity islands (PAIs) are a distinct class of genomic islands acquired by microorganisms through horizontal gene transfer. They are incorporated in the genome of pathogenic organisms, but are usually absent from those nonpathogenic organisms of the same or closely related species. These mobile genetic elements may range from 10-200 kb and encode genes which contribute to the virulence of the respective pathogen. Typical examples are adherence factors, toxins, iron uptake systems, invasion factors and secretion systems. Pathogenicity islands are discrete genetic units flanked by direct repeats, insertion sequences or tRNA genes, which act as sites for recombination into the DNA. Cryptic mobility genes may also be present, indicating the provenance as transduction.

One species of bacteria may have more than one PAI (i.e. Salmonella has at least 5). They are transferred through horizontal gene transfer events such as transfer by a plasmid, phage, or conjugative transposon.

An analogous genomic structure in rhizobia is termed a symbiosis island.

Properties

Pathogenicity islands (PAIs) carry genes encoding one or more virulence factors, including, but not limited to, adhesins, toxins, or invasins. They may be located on a bacterial chromosome or may be transferred within a plasmid. The GC-content of pathogenicity islands often differs from that of the rest of the genome,^[1] potentially aiding in their detection within a given DNA sequence.

PAIs are flanked by direct repeats; the sequence of bases at two ends of the inserted sequence are the same. They carry functional genes, such as integrases, transposases, or part of insertion sequences, to enable insertion into host DNA. PAIs are often associated with tRNA genes, which target sites for this integration event. They can be transferred as a single unit to new bacterial cells, thus conferring virulence to formerly benign strains.

Examples

• The UPEC P. fimbriae island contains virulence factors such as haemolysin, pili, cytotoxic necrosing factor, and uropathogenic specific protein (USP).^[2]
• Yersinia pestis high pathogenicity island I has genes regulating iron uptake and storage.
• Salmonella SP1 and SP2 sites
• Rhodococcus equi virulence plasmid pathogenicity island encodes virulence factors for proliferation in macrophages.
• The SaPI family of Staphylococcus aureus pathogenicity islands, mobile genetic elements, encode superantigens, including the gene for toxic shock syndrome toxin, and are mobilized at high frequencies by specific bacteriophages.^[3]

References

1. ^ Hacker J, Kaper JB., Pathogenicity islands and the evolution of microbes. Annu Rev Microbiol. 2000 ;54:641-79 http://www.ncbi.nlm.nih.gov/pubmed/11018140?dopt=Abstract
2. ^ Nakano M. et al. 2001 Structural and sequence diversity of the pathogenicity island of uropathogenic Escherichia coli which encodes the USP protein
3. ^ Lindsay, JA; Ruzin, A, Ross, HF, Kurepina, N, Novick, RP (1998 Jul). "The gene for toxic shock toxin is carried by a family of mobile pathogenicity islands in Staphylococcus aureus.". Molecular microbiology 29 (2): 527–43. PMID 9720870. 

External links

• BAC definition of pathogenicity

This microbiology-related article is a stub. You can help Wikipedia by expanding it. v t e