Abstract: This study aimed to screen new probiotics from naturally fermented yak milk. We separated and identified four Enterococcus durans strains by bacterial cultivation, gene sequence alignment and biochemical analysis. These four strains shared 99.4%–99.9% genetic homology by comparison of their 16S rRNA sequences with those of eight other E. durans isolates previously reported and were clustered into a separate branch by phylogenetic analysis. Among these isolates, E. durans SWUN5857 exhibited the most robust resistance to acidic and bile salts and could greatly adhere to intestinal mucus in different segments of the intestinal tract in Kunming mice, especially in lower intestines. Moreover, it inhibited the growth of pathogenic Escherichia coli ((17.0 ± 0.3) mm) and Salmonella ((18.0 ± 0.2) mm), and it was also sensitive to common antibiotics in vitro. Mice gavaged with SWUN5857 for a short term showed a significant body weight gain (P < 0.01) and an increase in immune organ indexes. Besides, this treatment also significantly promoted the animal humoral and cellular immunity level (P < 0.01) and enhanced the secretion of intestinal mucosa SIgA (P < 0.01). In conclusion, E. durans SWUN5857 can successfully adapt to the gastrointestinal condition and improve animal growth performance and immunological function, being, therefore, a promising candidate probiotic.

Key words: yak milk yogurt, Enterococcus durans, identification, probiotic properties