Probiotic consortiums: Structure and antagonistic activity against opportunistic bacteria and human normobiota (using the example of <i>Escherichia coli</i>) <i>in vitro</i>

Background . Using probiotic preparations based on consortia of microorganisms not only helps to restore the balance of the intestinal microbiota, but also increases the therapeutic effect of probiotics. Promising sources for obtaining probiotic consortia are milk products that have undergone natural fermentation with the help of spontaneously formed microbial consortia. The aim . To study the structure of five microbial consortia with probiotic properties from naturally fermented milk products and to assess in vitro their antagonistic activity against opportunistic bacteria and a representative of the human normobiota – Escherichia coli. Materials and methods . The structure of bacterial consortia was analyzed by sequencing methods. The antagonistic activity of the consortia was assessed by the disk diffusion method. Results . It has been established that the studied microbial consortiums are represented by Enterococcus spp. and Streptococcus spp. bacteria. In consortiums No. 1, No. 2, and No. 3, Enterococcus bacteria dominated, while in consortiums No. 4 and No. 5, Streptococcus dominated. Antagonistic activity was shown against four isolates of opportunistic bacteria: Klebsiella pneumoniae No. 493, Enterobacter hormaechei No. 372, Staphylococcus aureus No. 4 and Pseudomonas aeruginosa No. 25 IMB, as well as against one representative of the human normobiota – Escherichia coli No. 495. The highest growth delay zone is found in E. coli No. 495 isolate. Three test cultures (K. pneumoniae No. 509, E. coli ATCC25922 and P. aeruginosa No. 3 IMB) exhibited more dense growth around probiotic consortia. Conclusion . The results of the study showed that the effect of probiotic consortia differing in the composition of microorganisms can be neutral and bactericidal. The presence of antagonistic activity in the studied microbial consortia against multiresistant isolates of opportunistic bacteria is a prospect for creating probiotics with antibacterial properties.