Bile Salt Hydrolase and S‐Layer Protein are the Key Factors Affecting the Hypocholesterolemic Activity of Lactobacillus casei‐Fermented Milk in Hamsters

Scope Lactobacillus casei F0822‐fermented milk has exhibited significant hypocholesterolemic activity in hamsters in the previous study. Under this premise, the objective of this study is to further explore whether bile salt hydrolase (BSH) and S‐layer protein (SLP) of the strain have a significant influence on hypocholesterolemic activity of the fermented milk. Methods and results Independent and double interposon mutants of BSH and SLP genes are constructed from wild‐type L. casei F0822 via chromosomal insertion of chloramphenicol or/and erythromycin resistance genes based on double‐crossover homologous recombination. The mutants‐ and the wild‐type strain‐fermented milk is prepared (viable counts of approximately 8.0 × 108 colony‐forming units mL–1 each) and intragastrically administered to high‐cholesterol‐fed hamsters once daily at a dose of 1.25 mL d–1 for 28 d, respectively. Both the BSH‐deficient mutant‐ and the SLP‐deficient mutant‐fermented milk significantly (p < 0.05) increase serum total and LDL‐cholesterol levels in hamsters compared with the wild‐type strain‐fermented milk. However, only the BSH‐deficient mutant‐fermented milk could significantly (p < 0.05) increase hepatic total and esterified cholesterol levels in hamsters. Conclusion Both BSH and SLP have a significant influence on the hypocholesterolemic activity of L. casei F0822‐fermented milk in hamsters. Nevertheless, the BSH is greater than the SLP in this regard. Lactobacillus casei‐fermented milk is intragastrically administered to hamsters once daily at a dose of 1.25 mL d–1 for 4 weeks. It significantly decreases serum and hepatic cholesterol levels in hamsters by enhancing dairy fecal bile acid excretion levels, which is achieved by both hydrolysis of conjugated bile salts by the bacterial bile salt hydrolase and binding of free bile acids (hydrolysates of the conjugated bile acids) by the bacterial S‐layer protein.