Highly Adhesive Lactic Acid Bacteria (LAB) Strains Are Protective In Zebrafish Infected With Aeromonas Hydrophila By Evocation Of Gut Mucosal Immunity

As one species of probiotics, lactic acid bacteria play an important role in the innate immune system and homeostasis of the host, which is mainly regulated by gut mucosal immunity. To increase the knowledge of probiotic effects and potential mechanisms, we report on the use of the zebrafish model to investigate the in vivo colonization ability of previously characterized probiotic lactic acid bacteria (LAB) strains, Bacillus coagulans 09.712 and Lactobacillus plantarum 08.923, in comparison with that of three commercialized strains (Lactobacillus rhamnosus CGMCC 1.3724, Streptococcus thermophilus CGMCC 1.2471 and Bifidobacterium infantis CGMCC 1.2202). The results are concluded as follows:1. B. coagulans 09.712, L. plantarum 08.923 and L. rhamnosus CGMCC 1.3724 showed relatively strong biofilm formation abilities. The results indicated differential adhesion capabilities, and B. coagulans and L. plantarum strains exhibited a more robust adhesion capability based on fluorescence observation and plate culture method.2. Oral delivery of these two strains in zebrafish greatly improved gut epithelium integrity, as well as reduced recruitment and degranulation of mast cells under Aeromonas hydrophila NJ-1 challenge. By PAS staining, we found that B. coagulans 09.712 can stimulate the intestinal mucus layer to produce more neutral mucopolysaccharides for improvement of gut chemical barrier. The percentage of intraepithelial lymphocytes (IELs) in probiotic fed groups was significantly higher than those in the control after challenge (p< 0.001).3. In vivo, the abundance of IL-1β mRNA in B. coagulans- and L. plantarum-fed groups remarkably decreased as a function of time of post challenge, and that of TNF-a and IL-10 mRNA was high with the probiotic treatment. Taken together, our findings indicate highly adhesive strains of B. coagulans 09.712 and L. plantarum 08.923 have immunoregulatory and immunoprotective roles in effective stimulation of anti-inflammatory response and barrier regeneration within the mucosa to protect zebrafish against infection. In vitro, all of the expression of cytokines consistent with experimental results in vivo except for IL-1β mRNA.