ANTIMICROBIAL ACTIVITY OF CELL-FREE SUPERNATANTS FROM PROBIOTIC LACTIC ACID BACTERIA STRAINS AGAINST INTESTINAL OPPORTUNISTIC ISOLATES AND EFFECTS ON THEIR OWN PRODUCER STRAINS

Ivashko M.V. та Boyko N.V. (2025) ANTIMICROBIAL ACTIVITY OF CELL-FREE SUPERNATANTS FROM PROBIOTIC LACTIC ACID BACTERIA STRAINS AGAINST INTESTINAL OPPORTUNISTIC ISOLATES AND EFFECTS ON THEIR OWN PRODUCER STRAINS. Regulatory Mechanisms in Biosystems, 2025 (№3): Vol. 16. с. 1-10. ISSN 2519-8521

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Анотація

Metabolites produced by lactic acid bacteria (LAB) are involved in maintaining the balance of the human gut microbiota and play a role in inhibiting the growth of pathogens. The present study evaluated the antimicrobial activity of cell-free supernatants (CFS) obtained from ten probiotic strains of LAB. The antimicrobial activity was studied under varying pH conditions and afterheat and proteolytic treatment. Activity was evaluated against Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, Klebsiella oxytoca, and Candida albicans using the agar well diffusion method. The majority of the CFS exhibited a significant inhibitory effect against S. aureus, E. coli, and K. oxytoca, while inhibition of E. faecalis and C. albicans was predominantly observed for individual supernatants. Based on the results, the five most active CFS were selected for further research. The effect of CFS was also investigated in relation to probiotic strains of LAB, including their respective producer strains. It was found that the CFS of Lacticaseibacillus casei IMB 7412 strain exhibited the most pronounced inhibitory effect, both on its own viable cells and on other studied LAB strains. In contrast, Lactiplantibacillus plantarum IMB 7413 showed minimal changes in concentration under the influence of CFS. Additionally, the CFS of Lactobacillus bulgaricus A22 stimulated the growth of L. plantarum A. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the selected supernatants were determined by the micro-broth dilution method, which proved to be more sensitive than the agar well diffusion method, particularly in studies on E. faecalis and C. albicans. The antimicrobial activity was significantly dependent on pH, being highest under acidic conditions and decreasing or completely disappearing at neutral or alkaline pH. The heat resistance of the cell-free supernatants was relatively high, although heat treatment at 100 °C partially reduced their antimicrobial activity. Treatment with proteinase of the CFS of L. casei IMB 7412 resulted in a complete loss of antimicrobial activity, indicating the involvement of protein compounds in this effect. Thus, these results deepen our understanding of the antimicrobial effects of CFS from probiotic strains and their potential to modulate the intestinal microbiota.

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