The analysis of scientific publications concerning the features of etiopathogenesis and epidemiology of escherichiosis revealed that in Ukraine and in the countries of the world, human escherichiosis is quite common and constitutes one of the important problems of human medicine. The source of enteropathogenic E. coli is mainly productive farm animals, and the alimentary route is considered the most important in the mechanism of transmission of the pathogen. The detection of enteropathogenic E. coli in the process of food production in the chain "from field to table" can be carried out by various methods. The use of the fluorescent antibody (FBA) method for this purpose will have a positive impact on the effectiveness of the diagnosis and prevention of escherichiosis. Analysis of scientific publications and reports of FAO (The Food and Agriculture Organization) shows that control over the presence of enteropathogenic E. coli in food products is an important component of the One Health strategy. Development of express methods for indication and identification of enterotoxigenic E. coli is a relevant topic of scientific research. These include MFA. The diagnostic efficiency of MFA depends on the activity and specificity of Escherichia diagnostic sera. The purpose of the research is to assess the specificity of immune Escherichia serum obtained for the OH antigen of the enterotoxigenic β-hemolytic strain of E. coli. In the agglutination reaction (RA), the activity of bovine immune Escherichia serum to OH-antigens of a homologous strain of E. coli and the specificity to OH-antigens of heterologous strains of E. coli, as well as to OH-antigens of some species of bacteria of the Enterobacteriaceae family were studied. Bovine Escherichia serum was tested for specificity in the expanded RA with OH-antigens of heterologous strains of E. coli and strains of heterologous species of the Enterobacteriaceae family, in particular Salmonella enteritidis, Proteus vulgaris, Citrobacter freundii, Serratia marcescens, and Pseudomonas aeruginosa. It was found that the activity of Escherichia serum to OH-antigens of heterologous E. coli strains was high (titers from 1:1024 to 1:4096), and in some strains – almost the same as to OH-antigen of the homologous strain, for which the studied serum was obtained. This indicated a high specificity of the serum. At the same time, Escherichia serum contained agglutinins and to OH-antigens of heterologous bacterial species, in particular, to S. enteritidis – 1:64, P. aeruginosa – 1:32 and P. vulgaris, C. freundii and S. marcescens – 1:16. Adsorption of Escherichia serum with a suspension of inactivated microbial cells of S. enteritidis completely freed it from nonspecific agglutinins, without reducing its specific activity. The obtained Escherichia serum was highly active and specific to OH-antigens of heterologous E. coli strains. The presence of antibodies to OH-antigens of heterologous bacterial species was eliminated by the method of adsorption with a suspension of inactivated cells of the heterologous bacterial species.

Keywords: enterotoxigenic E. coli, immunization regimens, vaccine preparations, donor animals, agglutination reaction, bacterial antigens.