Synergy of Orally Delivered Probiotic and Vaccine for Enhanced Disease Resistance Against Virulent Aeromonas hydrophila in Channel Catfish

Abstract

Two feeding trials evaluated orally delivered vaccine and probiotic strategies against virulent Aeromonas hydrophila (vAh), the causative agent of motile Aeromonas septicemia in channel catfish (Ictalurus punctatus). In Trial 1, juvenile catfish received a probiotic (Bacillus velezensis AP193), an oral killed-vAh vaccine, or their combination for five weeks before vAh challenge. Vaccinated treatments exhibited the greatest survival, reducing cumulative mortality from 40% in controls to 16–19%. Treatments also altered immune gene expression and gut microbial composition, including increased abundance of beneficial genera such as Bacillus spp. and Cetobacterium spp. In a follow-up trial, the probiotic, vaccine, and an orange peel emulsifier (OPE) were evaluated alone and in combination. The probiotic alone provided the strongest protection, reducing mortality from 65% in controls to 31.7%, while combination treatments provided intermediate benefits. Across both studies, these treatments influenced gut microbial communities and immune responses without adverse effects on growth. These findings support the use of oral probiotics and vaccines as promising tools for sustainable disease management in catfish aquaculture.