Effect of an autologous preparation based on Streptococcus salivarius (S. salivarius) on oral cavity microbiota was investigated in participants of 8-month isolation study SIRIUS-2021 with the purpose of developing programs of preventing immunomicrobiological disorders. We investigated microbiota qualitative and quantitative dynamics, microbiological changes before and after consumption of the S. salivarius preparation using a bacteriologic technique, MALDI-TOF mass spectrometry, and microbial markers mass-spectrometry. Concentrations of secretion immunoglobulin A (slgA) and IL-8, IL-10 cytokines in oral liquid were determined with the immune-enzyme assay. It was found that the S. Salivarius-based autologous preparation had a favorable effect on the mouth microbiocenosis in all the participants in the study. © 2024 Slovo Ltd. All rights reserved.