Abstract:To select excellent probiotics of fish origin, tilapia fish (Oreochromis niloticus) was used as the experimental material to isolate and identify intestinal Bacillus and lactic acid Bacteria. The isolated strains were subjected to in vitro probiotic characteristics analysis, including antibacterial activity, acid tolerance, bile salts tolerance, artificial gastrointestinal fluid tolerance, hemolytic activity, and antibiotic susceptibility. The results showed that a total of 109 strains were isolated from tilapia fish intestine, including 79 strains of Lactobacillus and 30 strains of Bacillus. After a series of experiments, three strains of Lactococcus lactis were finally screened out. Biological characteristic studies indicated that all three strains exhibited no hemolytic activity. They showed a certain level of sensitivity to antibiotics and displayed tolerance to strong acids, bile salts, and artificial gastrointestinal fluids. Moreover, they demonstrated different antibacterial activities against aquatic pathogens. The three selected strains enriched the probiotic resources derived from fish, making them excellent candidates for fish-derived probiotics. Among them, strain R1 exhibited the highest tolerance to strong acids and artificial gastrointestinal juices, while strain R29 displayed the strongest bile salt tolerance. Further studies on their probiotic properties can be conducted to explore their probiotic effects as food-source probiotics.
