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In intestinal ecosystem, interchange of genetic material between different types of bacteria and other representatives of family Enterobacteriaceae results in development of types of normal colibacillus with genetic characteristics of pathogenicity. This occurrence can be considered as a theoretical substantiation for labeling such strains as pathobionts. The polymerase chain reaction was implemented to analyze 96 strains of different types of Escherichia coli (with normal and weak zymogenic activity and hemolytic activity) isolated from children with functional disorders of gastrointestinal tract. The purpose was to detect presence of gens coding capacity of toxin production (six1, stx2). In intestinal biotope of children, circulation of strains of Escherichia coli producing shiga toxin having no relation to pathogenic group being representatives of normal indigenous microbiota. The presence of gens stx1 and stx2 in various biochemical types of Escherichia coli permits establishing fact of forming of reservoir of potential pathogenicity in non-pathogenic forms of Escherichia coli. The presence of gen (verotoxin 1) in genome of various types of Escherichia coli isolated from one single biotope testifies possible horizontal transmission of factors of pathogenicity in intestinal biotope.

Aim: The detection by PCR of virulence markers in clinical strains of Escherichia coli strains producing the shiga-like toxin., Materials and Methods: Thirty-four strains of STEC isolated from patients with acute intestinal infection were studied. PCR with primers to following 10 genes of pathogenicity: rfbE, eaeA, iha, saa, stx1, stx2, cdt, cubA, ehx and espP was utilized. Susceptibility of isolated to antibiotics was determined. Presence of class I integrons in bacterial cells was assessed., Results: rfbE gene coding antigen of serogroup O157 was detected in 31 out of 34 isolates. Twenty-three (74.2%) strains of E. coli O157 had typical pattern of pathogenicity genes (rfbE, eaeA, stx1, stx2, ehx, and espP). In 12 out of 23 cultures (52.2%) sequence of iha gene was detected. Presence of cdt genes was revealed only in 2 clonical isolates belonging to serogroup O157 isolated in Moscow. Two out of 11 strains isolated in Tula region did not have rfbE and eaeA sequences but had sequences saa and subA, which were absent in other studied strains of STEC. Genes of class I integrons were not found in all studied strains although some of them were resistant to sulfonamides, tetracyclines, and aminoglycosides., Conclusion: Heterogeneity in pattern of pathogenicity genes was demonstrated in E. coli producing shiga-like toxin that points to circulation of different cultures among patients with acute intestinal infection, which is necessary to consider during analysis of clinical isolates.