This study aimed to evaluate the safety and probiotic properties of Bifidobacterium longum subsp. longum BL21 isolated from infant feces for use as a commercial probiotic strain.

Whole-genome sequencing; physiological and biochemical assessments; enzymatic assays; metabolite, antibiotic sensitivity, cell adhesion and cytotoxicity, and tolerance tests; and a 14-day oral toxicity study were conducted.

BL21 exhibited genetic integrity, and its genome lacked genes related to antibiotic resistance or virulence. It was found to be non-pathogenic, had efficient carbohydrate metabolism and mucin degradation ability, and was free from biogenic amines. It also showed susceptibility to antibiotics, strong cell adhesion, and resilience to adverse conditions. The aforementioned results confirm that BL21 is a functional probiotic strain with genetic stability, enzymatic capabilities, and non-pathogenic properties that mean it is safe for oral consumption, demonstrating that it is a promising candidate for probiotic applications.

The study demonstrates that BL21 is a genetically stable, non-pathogenic probiotic strain with metabolic potential. The strain lacks virulence and antibiotic resistance genes, and its resilience to gastrointestinal conditions, as well as the results of the 14-day oral toxicity study, suggest that BL21 is safe for oral consumption. However, further long-term studies and clinical trials are needed to confirm its safety and efficacy for therapeutic use.