In vivo assessment of possible probiotic properties of Bacillus subtilis and prebiotic properties of levan

Previously, Bacillus subtilis HMNig-2 and Bacillus subtilis MENO2 exhibited in vitro promising probiotic characteristics. They were tolerant to pH, bile salts, pancreatic enzymes, exhibited antimicrobial activity against pathogens and had ability to form biofilm. These strains also showed the highest levansucrase production and levan yield. In this study, the impact of the two Bacillus subtilis isolates and their levans were assessed in vivo in a mouse model. A novel correlation between the probiotic properties of the strains and their yielded levans was studied in terms of their effect on gut microbiota, immune system improvement and protection from Salmonella typhimurium infection that could cause liver inflammation and hepatic infiltration. Generally, the synbiotic strain (HMNig-2 and its levan) recorded the best results in lowering the coliform count by 1.5log while increasing Lactobacillus bacteria count in gut by almost 0.8log. Furthermore, it achieved the highest total IgA (22.4µg/mL), IgG (115.2µg/mL) and lysozymes concentrations (81.6U/mL) compared to 14.1 (µg/mL), 98.8 (µg/mL) and 64.5 (U/mL) of control, respectively indicating its beneficial role in immune system improvement. Results suggested that interaction between the probiotic strains with their levan could be used as synbiotics providing optimal liver protection against pathogen complications as shown by normal hepatic lobules and portal tracts. Levans of isolate B. subtilis HMNig-2 and B. subtilis MENO2 showed free radical scavenging activity of 48% and 40%, respectively. Results suggest the worth of studying further the possible applications of honey isolates and their products in health protection.