The information on the key pathogenicity factors of uropathogenic and enteropathogenic Escherichia coli, Shigella, Salmonella, Vibrio cholerae, Yersinia, Listeria and Helicobacter pylori is reviewed. The analysis of data on pathogenicity "islands" and "islets" of infective agents is given. The problems of the genetic control of pathogenicity factors and the functions of pathogenicity "islands", found in infective agents, are discussed.