Isolation of porcine intestinal Lactobacillus salivarius and antimicrobial potential of its biosurfactant

Lactobacillus salivarius (L. salivarius) is a probiotic widely colonized in the gastrointestinal tracts of humans and animals. Its biosurfactant (BS) exhibits antibacterial and antiviral activities, along with advantages such as biodegradability, non-toxicity, and stability. Porcine circovirus type 2 (PCV2) is a major pathogen in swine farms, causing immunosuppression or immune dysfunction. PCV2-positive herds exhibit elevated susceptibility, often accompanied by severe secondary bacterial infections. To explore novel antimicrobial biologics for enhancing swine immunity, this study isolated a biosurfactant-producing Lactobacillus strain from the intestines of PCV2-infected piglets using the calcium carbonate plate method, and analyzed the anti-microbial activity of the biosurfactant. A strain of biosurfactant-producing L. salivarius was successfully isolated from the ileum of PCV2-infected piglets. The extracted BS from the isolate demonstrated surface tension-reducing properties, forming spreading zones or dispersions on vegetable oil. The antimicrobial experiment showed that at the concentrations of 1.56 - 50 mg/mL, BS inhibited the growth of porcine E. coli and S. suis by 46.01% - 95.06% and 41.06% - 81.64%, respectively. Furthermore, BS of 6.25-12.5 mg/mL significantly inhibited PCV2 replication in PK-15 cells. These findings suggest that L. salivarius is a promising probiotic candidate for improving swine immune status and developing novel alternatives to conventional antimicrobial agents.