Heat-killed Lactococcus lactis subsp. lactis L8 ameliorates dextran sulfate sodium-induced colitis in mice

Lactococcus lactis subsp. lactis (L. lactis) is a common species of lactic acid bacteria (LAB). There is increasing evidence that probiotic L. lactis ameliorates experimental colitis in mice, whereas few studies have revealed the effects of the paraprobiotics, i.e., inactivated forms of bacteria. L. lactis L8 strain is a newly identified plant-derived LAB. The present study aimed to investigate the effects of heat-killed L. lactis L8 on dextran sulfate sodium (DSS)-induced colitis in mice. C57BL/6J mice were orally administered L. lactis L8 for 12 days. Colitis was induced by adding 3.5% DSS to the drinking water for 7 days. Mice were euthanized on day 12, and colon tissues and fecal samples were collected. Results demonstrated that administration of L. lactis L8 alleviated the clinical score of the colitis and the histological abnormalities. Additionally, L. lactis L8 led to a significant reduction in the level of colon tumor necrosis factor (TNF)-α. Administration of L. lactis L8 did not affect the gut microbial structure, whereas it altered the relative abundance of Clostridiaceae and Rikenellaceae in colitis mice. Our findings suggest that paraprobiotic L. lactis L8 has an immunomodulatory effect on intestinal inflammation in mice, providing important insight into the biological function of L. lactis L8.