Mastitis of infectious etiology cause huge economic damage in dairy farming, and milk loses its nutritional value due to the appearance of pathogenic bacteria in it. The article discusses the factors of pathogenicity of some pathogens of mastitis Str. pyogenes, Str. agalactiae, Str. disgalactiae, S. aureus. Streptococci possess such virulence factors as capsule, fimbriae (M-proteins), toxins, enzymes, staphylococci are capable to form a microcapsule and the biofilm, adhesins, enzymes, toxins, etc. Modern means of specific prevention are represented by polyvalent vaccines, often including inactivated pathogens of the following genera Streptococcus, Staphylococcus, Escherichia.

Streptococcal mastitis causes enormous economic damage in dairy farming. Milk loses its nutritional value due to the appearance of pathogenic bacteria in it that causes food toxicosis. In this study we used 28 isolates of streptococci isolated from cows with mastitis and endometritis. Of these, 38.9% belonged to S. agalactae, 33.3% to S. dysgalactae, and S. equi subsp. zooepidemicus - 22.2%. A small number of isolates -5.6% belonged to the species S. equi subsp. equi and S. uberis. in The test with mouse peritoneal macrophages shows that the antiphagocytic activity was 75% for isolates of S. zooepidemicus, 57% for S. agalactiae, and 64% for S. dysgalactiae. At the same time, the phagocytic number and phagocytic index were higher in the phagocytosis of the most strains featured with trypsin compared to the initial ones indicating to the antiphagocytic role of the pathogenic structures presented in them at the stage of bacteria capture. The numbers of factors of streptococci pathogenicity including M-proteins make them able to resist opsonization and phagocytosis