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We carried out studies aimed at studying immunogenicity of pathogen variants long-term persisted in the organism of wild animals and that have acquired antibiotic resistance, considering that the effect of anthropogenic factors on the causative agent of brucellosis (the use of antibiotics, disinfectants, ionizing radiation, mass vaccination, etc.) induces the appearance of altered forms of brucella with different immunological competence. 9 epizootic strains-isolates were used as test-strains, allocated: from wild reindeer (B.ranlifiri 0-172); from dogs (1005, S-122, S-227); from ermine (G-221); from wild foxes (P-278, P-271) from sow fetuses (B. suis 117); from hare (164), as well as virulent strain B.abortus 54; vaccine strain B.abortus 82 and antibiotic-resistant strain B.abortus 82C. The induction of antibiotic resistance of brucella was carried out by growing the original strain 82 on hepatic glucose-glycerol agar (PPGGA) containing various concentrations of antibiotic ciprolet from fluoroquinolones class, starting from the minimum concentration of ciprolet, then it was subcultured onto nutrient medium with a higher concentration of antibiotic, and brought to the state did when it stop to grow when the content of ciprolet was 5.10 and 20 mg/ml. Phenotypic properties of persistent and antibiotic-resistant strains of Brucella were studied by determining the cultural-morphological, bacteriological, immunological, and other research methods according to the generally accepted FAO/WHO scheme. Immunogenic properties of experimental cultures were studied in accordance with conventional methods by infecting immunized animals with a virulent strain of the pathogen. In vitro test system was used for the express method of immunogenicity evaluation of the studied strains according to the criterion of cytokine-inducing activity of antigens of experimental Brucella variants. The concentration of cytokines (KCF, IL-1β, TNF-α pg/ml) was determined by enzyme-linked immunosorbent assay technique using test systems manufactured by OOO "Cytokin" (Russia, St. Petersburg). It was established that the persistence of brucellosis pathogen in the body of domestic and wild animals of different sensitivity to this infection leads to significant changes in phenotypic properties of cultures (the degree of dissociation of phenotypic traits is 30%). The antibiotic-resistant version of B. abortus 82C vaccine strain was obtained, which has less agglutinogenic, but more pronounced immunogenic properties, by culturing original B. abortus 82 vaccine strain on a medium with sequentially increasing concentrations of new generation fluoroquinol antibiotic – ciprolet. The higher immunogenic activity of antibiotic-resistant variant of Brucella vaccine strain is associated with the antigen-induced synthesis of cytokines of classes KSF, IL-1 β, TNF-α.