The presence of fragments of genomes hlyA, hlyB, papAH, papC, sfaG, sfaA and kps MT, associated with the pathogenicity islands of Escherichia coli, in clinical strains of other genera of the family Enterobacteriaceae, has been experimentally evaluated with the use of PCR. The presence of DNA fragments specific to the known genes of the pathogenicity clusters of E. coli in representatives of the genera Citrobacter, Enterobacter, Hafnia, Klebsiella, Morganella, Proteus, Providencia, Serratia and Yersinia of rarely occurring groups has been established. In Enterobacteriaceae cultures isolated from the intestine amplicons homologous to hlyB were detected significantly less frequently than among strains of nonintestinal origin. In Enterobacteriaceae strains isolated in respiratory pathology amplicons of the pili gene (sfaG) were detected significantly more frequently than in collection cultures. The total evaluation of the detection rate of the genes of pathogenicity islands among Enterobacteriaceae clinical strains under study in comparison with E. coli showed that they occurred significantly less frequently. Klebsiella spp. were found to differ most essentially from E. coli as regards the occurrence of fragments of the genes of pathogenicity islands. The conclusion was made on the high probability of genetic exchange in DNA fragments between different species of bacteria with corresponding changes in their pathogenicity.