Bacteroides fragilis is a new generation of probiotics, and its probiotic effects on humans and some animals have been verified. However, research on B. fragilis in cattle is still lacking. In this study, 24 stool samples were collected from two large-scale cattle farms in Wuzhong, Ningxia, including 12 diarrheal and 12 normal stools. A non-toxigenic Bacteroides fragilis (NTBF) was isolated and identified by 16S rRNA high-throughput sequencing and named BF-1153; genome composition and genome functional analyses were carried out to reflect the biological characteristics of the BF-1153 strain. A cluster analysis of BF-1153 was performed using Mega X to explore its genetic relationship. In addition, Cell Counting Kit-8 (CCK8) was used to determine the toxic effects of the strain on human ileocecal colorectal adenocarcinoma cell line cells (HCT-8), Madin-Darby bovine kidney cells (MDBK), and intestinal porcine epithelial cells (IPECs). The results showed that BF-1153 conformed to the biological characteristics of B. fragilis. BF-1153 had no toxic effects on HCT-8, MDBK, and IPEC. Animal experiments have shown that BF-1153 has no toxic effects on healthy SPF Kunming mice. Notably, the supernatant of BF-1153 enhanced cell activity and promoted cell growth in all three cell lines. At the same time, a cluster analysis of the isolated strains showed that the BF-1153 strain belonged to the same branch as the B. fragilis strain 23212, and B. fragilis strain 22998. The results of the animal experiments showed that BF-1153 had a certain preventive effect on diarrhea symptoms in SPF Kunming mice caused by a bovine rotavirus (BRV). In summary, the strain BF-1153 isolated in this experiment is NTBF, which has no toxic effect on MDBK, HCT-8, and IPEC, and has obvious cell growth-promoting effects, especially on MDBK. BF-1153 promotes the growth and development of SPF Kunming mice when compared with the control group. At the same time, BF-1153 alleviated the diarrhea symptoms caused by BRV in SPF Kunming mice. Therefore, BF-1153 has the potential to be a probiotic for cattle.

Nontoxigenic Bacteroides fragilis (NTBF) is defined by the absence of the bft gene and corresponding B. fragilis toxin production; however, nontoxigenic status alone does not establish uniform safety or probiotic function. This review critically evaluates strain-level biological characteristics, safety, mechanisms, metabolites, and disease-model evidence. Selected strains and defined strain-derived preparations, including ZY-312, HCK-B3, NCTC 9343-derived polysaccharide A, and ZY-312-derived zwitterionic capsular polysaccharide preparation TP2, have shown immunomodulatory, barrier-associated, and microbial-community-modulating activities, predominantly in vitro and in animal models. Direct causal evidence is limited to specific strain–preparation–host–model combinations, whereas many changes in cytokines, tight-junction-associated proteins, microbial composition, and organic-acid profiles remain functional or associative. Protective effects have been reported in preclinical models of inflammatory bowel disease, necrotizing enterocolitis, antibiotic-associated diarrhea, Clostridioides difficile infection, and enterotoxigenic B. fragilis (ETBF)-associated tumorigenesis. However, findings are highly dependent on the strain, preparation, dose, administration timing, host, and model. Safety remains incompletely resolved because the absence of B. fragilis toxin (BFT) does not exclude opportunistic or systemic infection, antimicrobial-resistance mobility, bacterial translocation, permeability changes, or adverse effects during long-term administration. Metabolic effects may also be beneficial or adverse depending on the strain, host dietary and genetic background, and experimental context. Human evidence is primarily observational, and robust intervention trials are lacking. Accordingly, NTBF should be regarded as a heterogeneous group of strain-specific live-biotherapeutic candidates requiring rigorous strain-specific manufacturing, potency, dose, antimicrobial-susceptibility, and safety evaluation.