Abstract

Sustainable mitigation of piscirickettsiosis, the leading infectious cause of mortality in Chilean salmon aquaculture and a key driver of antibiotic dependence, demands green alternatives that fortify the intestinal health of fish. Here we show that brewer's spent grain (BSG), an abundant lignocellulosic by-product, can be upgraded into a functional feed additive through a fully aqueous, green-chemistry workflow comprising enzymatic hydrolysis with cellulase/hemicellulase, microwave-vacuum drying, and ultrasound-assisted water extraction. The process yields a solvent-free extract [bagasse extract-PBS (BEP)1860 mu g/mL gallic acid equivalents (GAE)] that preserves >= 90 % RTgutGC cell viability up to 35 mu g/mL GAE. A 24 h pre-exposure of rainbow trout intestinal epithelial cells to 5-25 mu g/mL GAE of BEP markedly enhanced the inflammatory response (il-1 beta and il-8 up-regulated up to 4.3-fold), strengthened barrier integrity (zo-1 up-regulated 3.1-fold), and activated antioxidant defenses (sod, gpx, gr elevated 2-5-fold). Importantly, pre-treatment with 25-100 mu g/mL GAE of BEP curtailed Piscirickettsia salmonis induced cellular lysis by similar to 45 % and reduced bacterial translocation across epithelial monolayers by similar to 1 log CFU, with the strongest protection against the prevalent EM-90-like genotype. This is the first report demonstrating that an agro-industrial residue can be converted, within a biocircular and sustainable-pharmacy framework, into an immunonutraceutical capable of simultaneously promoting the optimal immune system activation, the modulation of intercellular junctions, and the oxidative stress in this intestinal epithelial cell line. The present study suggests the use of BEP as a potential additive capable of modulating innate immune responses and contributing to future mitigation of the impact of P. salmonis infection. However, further studies are necessary to test this important issue for the aquaculture industry in Chile.