Impact of pathogenicity islands in bacterial diagnostics.

Pathogenicity islands (PAIs) are a distinct class of genomic islands (GEIs), which are acquired by horizontal gene transfer. PAIs harbour virulence genes and some, in addition, antibiotic resistance genes. More often genes conferring antibiotic resistance are encoded by GEIs not containing virulence genes. Both types of genetic elements are found in genomes of various human, animal and plant pathogens. There are PAIs and GEIs which are specific for a certain serotype(s), strain, or pathotype of a species. Furthermore, there are also PAIs which are more widespread and found in bacterial pathogens causing a certain pathogenic effect in the host. Even the lack of a certain PAI might be characteristic for a defined subspecies. Obviously, PAIs can be used as markers for diagnostic purposes to help identify a certain bacterial pathogen, subtype it, estimate the pathogenic potential, and in some cases predict its antibiotic resistance. This all might be achieved for known PAIs/GEIs without cultivating the microorganism of interest by employing PCR and/or DNA-chip technology. Even yet unknown PAIs can be identified in silico if the genome sequence of the bacterial pathogen under investigation is known. The more PAIs and antibiotic harbouring GEIs are identified and characterized the greater will be the benefits also for diagnostics.