Patogeenseid

Patogeenseid, or pathogenicity island, is a discrete genetic element in bacteria that carries clusters of virulence genes. These islands are typically acquired through horizontal gene transfer and can convert a nonpathogenic strain into a pathogen by providing functions such as secretion systems, adhesins, toxins, or immune evasion factors.

Molecular features: Patogeenseid often show a distinct nucleotide composition compared with the rest of the genome, and are frequently flanked by tRNA genes or direct repeats. They may contain mobility genes such as integrases, transposases, or remnants of phage elements, enabling excision or transfer. They frequently appear as genomic islands with a mosaic structure.

Role in virulence: Islands contribute to initial colonization, tissue invasion, host immune modulation, and disease symptoms. Their expression is tightly regulated and may depend on environmental signals and regulatory networks in the host.

Origin and evolution: Pathogenicity islands arise by horizontal transfer from other organisms and can be maintained in the genome by selection. They often accumulate additional virulence factors or lose genes, leading to variation among strains.

Examples: Salmonella pathogenicity islands SPI-1 and SPI-2 encode type III secretion systems; the LEE pathogenicity island in enteropathogenic E. coli encodes a type III secretion apparatus; Vibrio cholerae pathogenicity island VPI-1; Staphylococcus aureus pathogenicity islands SaPI carry toxin genes.

Clinical relevance: Identifying patogeenseid helps in understanding virulence potential, epidemiology, and design of vaccines or therapeutics. They illustrate how virulence traits can be gained and spread among bacteria.