A Novel Lactobacillus acidophilus Strain Isolated from a 2-Month-Old Shiba Inu: In Vitro Probiotic Evaluation Safety Assessment in Mice and Whole-Genome Sequencing Analysis

Owing to their remarkable biological activities and health benefits, probiotics have gained widespread application in enhancing pet health and welfare. Host-derived probiotics are considered optimal due to their unique digestive tract environments. This study isolated <i>Lactobacillus acidophilus</i> L1 from the feces of a 2-month-old Shiba Inu puppy and conducted a comprehensive evaluation of its potential as a probiotic candidate for pet health. Strain L1 demonstrated high tolerance to acidic conditions (survival rates of 90.41%, 92.90% and 98.81% at pH 2, 2.5, and 3.0, respectively) and bile salts (survival rates of 98.05%, 95.68%, and 82.21% at 0.1%, 0.2%, and 0.3% concentrations, respectively). Adhesion to Caco-2 intestinal epithelial cells reached 38.33%, with hydrophobicity of 97.81% and auto-aggregation of 32.28%. L1 also displayed pronounced antioxidant activity, with DPPH and ABTS radical scavenging rates of 71.15% and 83.20%. Both the bacterial suspension and the cell-free supernatant had potent inhibition of pathogenic bacteria, while the strain showed a non-hemolytic phenotype and remained sensitive to clinically relevant antibiotics (e.g., penicillin). On the other hand, animal experiments conducted in ICR mice (randomly divided into four groups) demonstrated that oral administration of L1 had no toxic effects on the mice and increased serum SOD and CAT levels, while reducing MDA levels. Furthermore, whole-genome sequencing revealed that L1 is 2,106,895 bp in size and contains 2098 coding sequences, two CRISPR arrays, ten genomic islands, and two prophage regions. Collectively, the in vitro and in vivo data presented here indicate that <i>L. acidophilus</i> L1, originally isolated from canine feces, supports further evaluation as a candidate strain for incorporation into functional pet foods.