Abstract
INTRODUCTION: Aeromonas veronii remains a pervasive aquatic pathogen precipitating catastrophic economic depletion and threats to global food security. Conventional therapeutic modalities are constrained by inadequate stability, prohibitive costs, and biosafety risks. METHODS: To address such challenges, an engineered Lactobacillus casei strain was developed to constitutively express the A. veronii outer membrane protein OmpAI through a tandem promoter system to ensure optimized antigen delivery. RESULTS: Anal intubation with engineered L. casei in Channa argus stimulated compartmentalized mucosal immunity, evidenced by a six-fold elevation in hindgut IgT transcripts, significant infiltration of IgT(+) B cells, and pIgR mediated transcytosis, synchronized with systemic IgM activation. The probiotic treament accelerated pathogen clearance, improved survival rates to 42.9% compared to 12.5% in control group, and reorganized the commensal microbiome through a specific enrichment of beneficial Firmicutes. DISCUSSION: This study elucidated a novel engineered-probiotic mucosal vaccination strategy for teleosts, providing a noninvasive, mucosal targeted immunoprophylactic strategy to decrease antibiotic dependency in aquaculture.