Probiotic Lactobacillus plantarum SHY21-2 protected zebrafish against Aeromonas hydrophila infection by maintaining intestinal barrier integrity, inhibiting inflammatory and oxidative stress responses, and regulating intestinal microbiome

Lactic acid bacteria are generally regarded as an effective alternative to antibiotics in aquaculture farming, especially Lactobacillus strains, which are safe and have probiotic potential. However, the mechanism of action of probiotic Lactobacillus in protecting fish against Aeromonas hydrophila infection remains unclear. In this study, a strain of Lactobacillus plantarum SHY21-2, was investigated for its safety and probiotic properties using a combination of phenotypic and whole-genome analysis. The results revealed that SHY21-2 has good safety, antimicrobial activity, and multiple probiotic properties, including tolerance to acid and bile salts, adherence to intestinal epithelial cells, and effective immunomodulatory and anti-inflammatory potential. Furthermore, 240 zebrafish were randomly divided into 4 groups. After 1 week on a basal diet with or without SHY21-2, all zebrafish were exposed to water with or without A. hydrophila AH40 for 12 h; finally, all zebrafish were transferred to freshwater and fed the basal diet for 5 days. The results showed that supplementation with SHY21-2 alleviated the symptoms of zebrafish infected with A. hydrophila, significantly reduced mortality, inhibited intestinal and muscle inflammation, maintained intestinal barrier integrity, and alleviated hepatic oxidative stress responses. Notably, AH40-infection induced variations in microbial diversity and enriched harmful bacteria, such as unclassified-f-Parachlamydiaceae, Rhodococcus, unclassified-f-Microbacteriaceae, and Bosea, whereas supplementation with SHY21-2 reversed this result and significantly increased the abundance of beneficial bacteria, such as Lactiplantibacillus, Leucobacter, and Gemmobacter. In conclusion, these results suggest that SHY21-2 can effectively protect zebrafish against A. hydrophila infection and is an appropriate candidate probiotic for the aquaculture industry.