A mobile genetic element in the chromosome of some bacteria that contains a cluster of genes responsible for the disease-causing properties of that particular bacterial strain or species. The element becomes integrated into the host cell’s chromosome following lateral gene transfer from other bacteria by means of bacteriophage, transposons, or plasmids. The virulence genes of the PAI might, e.g. endow the bacterium with the ability to synthesize new enzymes or toxins, or make it resistant to antibiotics, and are significant in determining its potential to cause disease in higher organisms.