Adherence capability and safety assessment of an indigenous probiotic strain Lactobacillus rhamnosus MTCC-5897

With the growing interest in probiotic microorganisms based on their well established immense health benefits, the present investigation was aimed to assess the adhesion potential and safety of probiotic Lactobacillus rhamnosus MTCC- 5897 (LR) before it can be put into a probiotic formulations. L. rhamnosus showed an adhesion index of 166.7 ± 11, which was further confirmed by scanning electron microscopy and relative expression of mucus binding protein (Mub) and mucus adhesion promoting protein (Map-A) genes. In vitro safety assessment by tetrazolium dye reduction, neutral red and lactate dehydrogenase (LDH) release assays revealed unchanged metabolic activity of Caco-2 cells even when incubated with L. rhamnosus ranged between 10⁶-10¹⁰ cfu/mL for 24 h. Similarly, a moderate increase in bile salt hydrolase (bsh) expression (6.84 ± 0.73 and 3.42 ± 0.39 folds in 1% and 3% bile medium respectively) further proved its safety towards normal lipid digestion and absorption. Moreover, L. rhamnosus feeding to mice (10⁷, 10⁹, 10¹¹ and 10¹³ cfu/animal/d) repetitively for 28 days revealed no adverse effects on parameters of general animal health status including body weight, organ indices, plasma glucose, liver malondialdehyde (MDA), serum aspartate amino transaminase (AST), cholesterol, triglycerides, high-density lipoprotein (HDL). Similarly, significant (p ≤ 0.05) reduced activities of serum alanine amino transaminase (ALT) and LDH on continuous probiotic feeding were also indicative of normal liver/kidney functions as they were in normal range for mice. Further, insignificant changes in macrophage chemoattractant protein (MCP-1) in intestinal fluid irrespective of bacterial dose fed along with significant reduction (p ≤ 0.05) of tumor necrosis factor-α (TNF-α) at much higher dose (10¹³ cfu/animal/d) also confirmed safe response of probotic L.rhamnosus against inflammation. To conclude, the results obtained under in vitro and in vivo studies has established the Lactobacillus rhamnosus as safe and non-toxic to weaning mice as well as human epithelial cells and thus may be used as a safe food additive.