AimsTo increase the knowledge of probiotic effects and potential mechanisms, we report on the use of the zebrafish model to investigate the invivo colonization ability, as well as the protective effects associated with gut mucosal immune barrier and responses against Aeromonas hydrophila infection of previously characterized probiotic lactic acid bacteria (LAB) strains, Bacillus coagulans 09712 and Lactobacillus plantarum 08923, in comparison with that of three commercialized strains. Methods and ResultsThe results indicated differential adhesion capabilities, and B.coagulans and Lact.plantarum strains exhibited a more robust adhesion capability based on fluorescence observation. Oral delivery of these two strains in zebrafish greatly improved gut epithelium integrity, as well as reduced recruitment and degranulation of mast cells under Aer.hydrophila challenge. The percentage of intraepithelial lymphocytes (IELs) in probiotic fed groups was significantly higher than those in the control after challenge (P<0001). We also found that the abundance of IL-1 mRNA in B.coagulans- and Lact.plantarum-fed groups remarkably decreased as a function of time of post challenge, and that of TNF- and IL-10 mRNA was high with the probiotic treatment. ConclusionsOur findings indicate highly adhesive strains of B.coagulans 09712 and Lact.plantarum 08923 have immunoregulatory and immunoprotective roles in effective stimulation of anti-inflammatory response and barrier regeneration within the mucosa to protect zebrafish against infection. Significance and Impact of the StudyOur work will further support zebrafish as a powerful model to better understand molecular definition of probiotic effects, as well as the probiotic potential of B.coagulans 09712 and Lact.plantarum 08923 of interest to the food industry.