In vitro screening and identification of Lactobacilli with potential probiotic characteristics from breast milk and infant feces

The infant gut microbiota plays a crucial role in shaping long-term health outcomes. Early microbial colonization is primarily influenced by the mode of delivery and breastfeeding. Studies have demonstrated that probiotic effects are strain-specific. In this study, 83 bacterial strains were isolated from breast milk and infant stool samples, and sequencing analysis identified 18 Lactobacilli strains. Among them, 50% were isolated from infant feces, while the remaining nine strains, all Lactobacilli gasseri , were derived from breast milk. The probiotic properties and safety of these Lactobacilli strains were evaluated through a series of experiments, including acid and bile salt tolerance, antibiotic resistance, antibacterial activity, adhesion to HT-29 cells, and comparative genome analysis. Results showed that 77.8% of the strains exhibited strong tolerance to simulated gastric fluid (pH 3.0), with survival rates exceeding 60%. Under simulated intestinal conditions (pH 8.0), the highest survival rate observed was 34.59%, while three strains displayed intolerance. Additionally, all strains were capable of utilizing at least two carbohydrate sources beyond glucose and were sensitive to at least two types of antibiotics. Notably, Lacticaseibacillus rhamnosus demonstrated superior sugar utilization and antibiotic sensitivity. Furthermore, the adhesion ability of 15 strains to HT-29 cells ranged from 5.75% to 23.39%, with L. gasseri MR18L3 exhibiting a notable adhesion rate of 22.36%. Overall, L. gasseri MR18L3 and L. rhamnosus BB6L9 demonstrated promising probiotic potential and safety profiles, suggesting their potential application in the development of functional probiotics for infants and young children.