The effect of various carbohydrate sources on the antagonistic activity of probiotic strains Lactobacillus paracasei and Bifidobacterium longum against opportunistic intestinal pathogens

Introduction. Carbohydrates, including dietary sugars and prebiotic oligo- and polysaccharides, can influence on the functional activity of probiotic bacteria by modulating their metabolic processes. An important property of prebiotics is the selective activation of endogenous protective populations of intestinal microflora, which helps to suppress the growth of pathogenic and opportunistic microorganisms. However, the specificity of various prebiotic supplements for specific exogenous probiotic microorganisms remains unclear. Probiotics can be components of a wide range of foods and dietary supplements, so it is important to understand how various nutritional substrates influence on their metabolic and functional activity. This knowledge will enable the development of more effective products and supplements aimed at maintaining intestinal bacterial balance. ”In vitro” studies allow evaluating the effects of individual components on probiotic strains. In this work, the effect of various carbohydrate substrates on the antagonistic activity of exogenous probiotic strains Lactobacillus paracasei and Bifidobacterium longum against a number of opportunistic microorganisms was studied.Objective — to study the effect of various carbohydrate substrates, including well-known prebiotics, on the antagonistic activity of probiotic strains studied against opportunistic pathogens. The choice of a carbohydrate that improves the competitive properties of probiotic strains of L. paracasei and B. longum.Materials and methods. The antagonistic activity of two probiotic strains against seven pathogenic microorganisms was studied in the presence of nine different carbohydrate substrates using a two-stage cultivation method in a combined system.Results. Probiotic strains were established to exhibit selective antagonistic properties against the same pathogen, depending on the presence of a particular carbohydrate source. For example, lactose and sucrose were found to contribute to an increase in the degree of antagonistic activity of lactobacilli against Staphylococcus aureus from moderate to high relative to the control and other substrates, and inulin and FOS suppress the competitive properties of this strain relative to Pseudomonas aeruginosa. The studied strain of Bifidobacterium longum exhibits moderate antagonistic activity against E. coli and C. jejuni, however, a number of substrates (sucrose, mannitol, inulin, chitosan) are capable of inhibiting this property. At the same time, substrates such as lactose, maltose, sucrose, chitosan, and N-acetyl-D-glucosamine increase antagonistic activity from low to moderate against K.pneumoniae, P.aeruginosa, and A.baumannii. Based on the data obtained, it can be assumed that N-acetyl-D-glucosamine (NAG), mannitol, maltose, and lactose are of interest as substrates that increase the antagonistic potential of the studied strains against a number of opportunistic pathogens.Limitations. Antagonistic activity in co-cultivation of probiotic strains has not been studied. It is also difficult to assess the functional properties of the studied strains depending on the prebiotic in the gastrointestinal tract. In addition, the effect of the concentration of carbohydrate substrates used in the work on the antagonism of target probiotic strains has not been studied.Conclusion. We have identified a significant effect of the carbohydrate component on the antagonistic properties of the probiotic strains studied, which can be further taken into account in the development of probiotic compositions, synbiotics, and functional foods.Compliance with ethical standards. The study does not require the submission of a conclusion from the biomedical ethics committee or other documents.Contribution: Kalashnikova I.G. – concept and design of research, collection of material and data processing, writing text, conducting research; Nekrasova A.I. – concept and design of research, editing; Gritsyuk O.V., Fedets Z.E., Pankova M.N. – conducting research, methodology development; Zagainova A.V. – providing research, project administration; Zhernov Yu.V., Makarov V.V. – definition of the concept, attraction of financing, provision of research; Yudin S.M. – attraction of financing, provision of research. All authors are responsible for the integrity of all parts of the manuscript and approval of the manuscript final version.Conflict of interest. The authors declare no conflict of interest.Funding. The work was performed within the framework of the state task No. 388-00154-22-00 “Creation of micellar probiotics of a new generation for targeted changes in the composition of the human microbiota in chronic non-communicable diseases”.Received: October 2, 2025 / Revised: November 24, 2025 / Accepted: December 2, 2025 / Published: January 15, 2026