Antagonistic activity of Bacillus subtilis bacterial strains isolated from the microbiota of wild ungulates of Yakutia

The aim of the study is to investigate the antagonistic activity of six collection strains of B. subtilis bac-teria against S. aureus, E. coli, and S. enteritidis in order to select promising strains as the basis for a pro-biotic feed additive. The antagonistic activity of six new strains of B. subtilis bacteria isolated from the microbiota of wild ungulates in Yakutia was studied for the first time. The antagonistic activity of B. subtilis bacterial strains was determined by the delayed antagonism method using perpendicular streaks. Two isolates of S. aureus spp. were used as test cultures: isolate of E. coli spp. and S. enteritidis 13076. The studies to select promising strains as the basis for a probiotic feed additive were carried out in two stages: Stage 1 – studies of the antagonistic activity of six bacterial strains, from which the most powerful antagonists against opportunistic microorganisms were selected; Stage 2 – sowing on an experimental nutrient medium and assessing its effect on the antagonistic activity of the selected strains of B. subtilis bacteria in relation to two isolates of S. aureus. The activity of B. subtilis strains was assessed by the zone of inhibition of growth of opportunistic microorganisms. The studied strains of B. subtilis bacteria demon-strated pronounced antagonism, varying from 8 to 18 mm against isolates of Staphylococcus aureus spp., less pronounced – from 2 to 7 mm against the isolate of E. coli spp. and the absence or manifestation of weak antagonism (from 0.5 to 1 mm) against S. enteritidis 13076. Based on the obtained data, two promi-sing bacterial strains were selected for the development of a probiotic supplement: B. subtilis 11-4/1k and B. subtilis 27-7/1l. The bacterial strains B. subtilis 27-7/1l and B. subtilis 11-4/1k have undergone interna-tional patent deposition at the Bioresource Center — All-Russian Collection of Industrial Microorganisms (BCR VKPM) of the National Research Center Kurchatov Institute. The bacterial strains have been as-signed registration numbers: B. subtilis 27L VKPM B-14800 (deposit date 09/06/2024), B. subtilis 11K VKPM B – 14816 (deposit date 09/06/2024).