Comprehensive assessment of Enterococcus faecalis SN21-3: Probiotic features and safety evaluation for potential animal use

In this study, the probiotic characteristics of Enterococcus faecalis SN21-3 were explored by genotype and phenotype, and the safety of this strain was evaluated in vitro and vivo. The complete genome sequence of E. faecalis SN21-3 revealed basic genetic information and corresponding genes underlying its probiotic characteristics. In vitro experiments were performed with E. faecalis SN21-3, which showed prominent antimicrobial activity and excellent abilities of resistance to simulated gastrointestinal fluid, cholesterol assimilation, adhesion, and antioxidant. In addition, E. faecalis SN21-3 was susceptible to the most common antimicrobial agents, did not contain transferable resistance gene and pathogenic gene, and did not perform haemolysis reactions and gelatinase activity in vitro. Furthermore, in vivo experiments demonstrated that feeding E. faecalis SN21-3 to broilers for 28 days did not significantly affect their normal growth or blood biochemistry parameters. Moreover, H&E staining showed no evidence of lesions in the heart, liver, spleen, or kidney of the broilers. No migration of E. faecalis SN21-3 was observed in the heart, liver, spleen, kidney, or blood samples during the feeding trial, indicating that the bacteria did not cause infections. In summary, E. faecalis SN21-3 exhibits numerous probiotic characteristics and is sufficiently safe for use as a novel animal probiotic.