Probiotic potential of three Enterococcus spp. isolated from raw milk: An in vitro assessment

Abstract

In this study, three strains of Enterococcus spp. (E. durans 19, E. durans 77, and E. faecalis 52), isolated from raw milk and confirmed to lack virulence genes (asa1, gelE, cylA, esp, and hyl), were investigated. The biological activities of these strains, including EPS production, antimicrobial and antioxidant properties, auto-aggregation, co-aggregation, hydrophobicity, anti-biofilm activity, acid and bile tolerance, and cholesterol assimilation, were evaluated. Strains showed high exopolysaccharide production, and the highest EPS production was observed in E. durans 19 (440 mg/L). The maximum microbial inhibition zone of 4.50 mm was detected with E. durans 77 against S. aureus ATCC 25923. The antioxidant activity of strains was evaluated by three methods (2.2-Diphenyl-1-picrylhydrazil (DPPH), superoxide anion, and hydroxyl radical scavenging activity. E. durans 77 exhibited the highest antioxidant activity of 41.65%, as determined by the DPPH method. Strains exhibited close auto-aggregation ability (58%, 56%, and 55%) of each other. E. durans 19 exhibited the strongest coaggregation capacity (65%) against P. aeruginosa ATCC 27853. Three different solvents (chloroform, ethyl acetate, and xylene) were used to designate the hydrophobicity activities of the strains. E. durans 19 and E. faecalis 52 strains exhibited the highest hydrophobicity in ethyl acetate at 83% and 85%, respectively, whereas E. durans 77 demonstrated in chloroform solvent (77%). Antibiofilm activities of three strains against S. aureus ATCC 43300 were examined and values were detected as 29.41–34.17%. In this study, the survivability of the strains to low pH (2.0, 3.0, 4.0, and 6.2) and various bile concentrations (0, 0.06, 0.15, and 0.30) conditions were investigated, and it was observed that the bacterial viability decreased as the acidity and bile concentration in the medium increased. Cholesterol removal capability was determined to a range of 29–40% and cholesterol precipitation between 22.5 and 28.4 μg/mL.