Safety Assessment and Probiotic Potential of a Novel Species Lactobacillus xujianguonis

<b>Background</b>: Some lactobacilli strains have been documented to cause bacteremia and sepsis in immunocompromised or critically ill hospitalized patients, challenging the universally presumed safety of lactobacilli. Therefore, strain-specific risk assessments are required for the use of <i>Lactobacillus</i> as a probiotic. <i>Lactobacillus xujianguonis</i>, a novel <i>Lactobacillus</i> species isolated from <i>Marmota himalayana</i>, has probiotic potential but lacks safety data. <b>Objective</b>: To evaluate the preclinical safety of <i>L. xujianguonis</i> for food-grade use. <b>Methods</b>: Systematic safety assessment includes <i>in vitro</i> studies and oral toxicity studies. <i>In vitro</i> studies encompassed gastrointestinal tolerance, auto-aggregation and pathogen inhibition, antibiotic susceptibility, and hemolysis/gelatinase activity assays. Oral toxicity studies contained acute single-dose and repeated-dose 28-day oral toxicity studies in mice based on the OECD toxicity study guidelines. <b>Results</b>: <i>L. xujianguonis</i> strains HT111-2 and 06-2 demonstrated certain probiotic traits, including high acid/bile tolerance, strong auto-aggregation, and antimicrobial activity against common human gastrointestinal pathogens. <i>In vitro</i> safety assessments showed susceptibility to nine antibiotics and absence of hemolytic/gelatinase activity. Acute oral exposure (1 × 10¹¹ CFU/kg) induced no mortality, clinical abnormalities, or organ toxicity. Subchronic 28-day administration (multiple doses) showed absence of adverse clinical signs with body weight stability and no hematological, biochemical, or histopathological deviations in C57BL/6 mice. Inflammatory and immunological markers remained unaffected. Histological staining results and transcriptional level validation revealed no evidence of intestinal tissue damage. <b>Conclusions</b>: This study provides preliminary evidence of the safety of <i>L. xujianguonis</i>, supporting its advancement to functional research.