Probiotic potential of Lactobacillus brevis and Lactococcus lactis isolates from cottage cheese whey

Currently, the search for new promising strains of lactic acid bacteria (LAB) for use as probiotic supplements in animal husbandry farming is a pressing issue. Cottage cheese whey, a by-product of dairy production characterized by low pH values and a specific chemical composition, serves as a natural habitat for phenotypically resistant strains potentially capable of surviving in the gastrointestinal tract of animals. In this study, two LAB strains, Lactobacillus brevis and Lactococcus lactis , were isolated and identified from a cottage cheese whey sample. A comprehensive assessment of their probiotic potential included the determination of antagonistic activity against Escherichia coli test strains, resistance to various pH values (2.0–8.0) and bile concentrations (10–40%), antibiotic susceptibility, as well as adhesive properties (autoaggregation, cell surface hydrophobicity, and biofilm formation ability). The results showed that both strains exhibit high antagonistic activity against E. coli . Meanwhile, L. lactis demonstrated very high efficacy (growth inhibition zones exceeding 20 mm) against two of the three test cultures. The most significant differences between the strains were revealed in the assessment of their resistance to gastrointestinal factors: L. brevis exhibited high resistance to low pH 2.0 (maintaining viability at >10⁸ CFU/mL) and high bile concentrations (up to 30%), whereas L. lactis was more sensitive to these stress factors. Both strains displayed multiple natural antibiotic resistance, which is typical for "wild" LAB strains; however, the antibiotic resistance profile of L. lactis was broader. In the assessment of adhesive properties, both strains were found to possess high cell surface hydrophobicity (>97%), with L. lactis significantly surpassing L. brevis in autoaggregation ability (86% vs. 41%) and moderate biofilm formation. The results of this comprehensive evaluation of the probiotic properties of strains isolated from cottage cheese whey open up prospects for the development of effective multi-strain probiotic preparations for farm animals.