Determination of the drug Fagomast effectiveness with different titers of Phage SAvB14

Treatment of bacterial infections with bacteriophages is one of the alternative methods. However, the use of freely dispersed bacteriophages for treatment causes their inactivation under physiological conditions. Therefore, it is important to consider the concentration of bacteriophages in phage therapy. The aim of study – to determine the optimal titer of bacteriophage Phage SAvB14 in the drug Fagomast for the effective treatment of subclinical mastitis in cows caused by Stapholococcus aureus var. bovis. For research to determine the optimal therapeutic dose of the bacteriophage drug Fagomast in vitro, groups of animals were formed on the principle of analogues. Controls were animals treated with an antibiotic-based drug according to the instructions for use. Cows of the first experimental group were used samples of the drug with a titer of Phage SAvB14 10-7 BFU/ml, the second experimental group with a titer of 10-8 BFU/ml and the third group – 10-9 BFU/ml. It was found that all batches of Fagomast (81.8 - 92.8%) show good therapeutic efficacy, but the duration of treatment of animals was different. When using the drug Fagomast with a phage titer of 10-9 BFU/ml, it is shorter by 1 day than cows that were injected with a phage titer of 10-8 BFU/ml and 1.5 days compared with cows of the first group, which were injected with a phage titer of 10-7 BFU/ml. The results of the therapeutic efficacy of Fagomast with a bacteriophage titer of 10-8 and 10-9 BFU/ml in the drug are confirmed by the reaction with Mastidine, which after 48 hours was assessed as doubtful, and after 72 hours – as negative, as with antibiotic treatment. The content of S. aureus in the secretion of cows 12 hours after administration of the drug with a phage titer of 10-9 BFU/ml decreased 6 times (P ≤ 0.05), and after 48 hours 40 times (P ≤ 0.05), and after 60 hours of therapy did not stand out at all. The titer of bacteriophages remained at the level of 10-7 BFU/ml, and when the number of susceptible bacteria decreased to zero it decreased by 2 orders of magnitude. Thus, it can be said that maintaining a higher concentration of phage virions leads to better distribution of phages in the breast, and thus to improved binding of phages to host cells and their destruction. Key words: bacteriophages, Staphylococcus aureus, phagotherapy, bacteriophage drug, mastitis, cows.