Bioactive metabolites of Lactobacillus plantarum SB8 mitigate deltamethrin-induced oxidative stress and immune dysregulation in Nile Tilapia (Oreochromis niloticus)

Synthetic pesticides such as deltamethrin (DLM) pose severe risks to aquatic organisms, causing oxidative damage, immune dysregulation, and growth impairment in farmed fish. In this study, we investigated the protective role of Lactobacillus plantarum SB8, focusing on the bioactive metabolites present in its cell-free supernatant (CFS). In vitro, assays demonstrated that SB8 metabolites exerted strong antibacterial activity against Aeromonas hydrophila and Pseudomonas fluorescens. In vivo experiments with Nile tilapia (Oreochromis niloticus) revealed that dietary supplementation with SB8 markedly attenuated DLM-induced hematotoxicity, restoring leukocyte counts and protein profiles. Moreover, SB8 supplementation normalized antioxidant enzyme activities (SOD, CAT, GPx), reduced lipid peroxidation (MDA levels), and downregulated pro-inflammatory cytokines (IL-1β, IL-6) in liver tissue. GC–MS analysis of SB8 L. plantarum metabolites identified components such as lactic acid, acetic acid, phenolic derivatives, exopolysaccharides, peptides, and bacteriocins, which support antioxidant, antimicrobial, and immunomodulatory activities. These findings highlight that bioactive compounds secreted by L. plantarum SB8 can counteract pesticide-induced oxidative stress and inflammation, providing a promising molecular strategy for mitigating chemical toxicity in aquaculture species.