Dietary yeast improves zebrafish immunity and survival against Aeromonas infection

This study aimed to evaluate the potential of autolysed Cyberlindnera jadinii yeast (ACJ) as a functional feed additive to enhance intestinal immunity and disease resistance in zebrafish (Danio rerio) following a bacterial challenge with Aeromonas salmonicida subspecies salmonicida. Zebrafish were fed either a control or a ACJ-supplemented diet for 2 weeks, followed by bath exposure to A. salmonicida subspecies salmonicida. To achieve this, post-challenge responses were assessed using a multi-method approach, including mortality tracking, bacterial detection by qPCR, histology, immunohistochemistry, and proteomic analyses (iTRAQ and SWATH-MS). Fish fed the ACJ diet exhibited significantly lower mortality (0.8 %) compared to the control group (7.5 %) (P = 0.0104, log-rank test). PCR analysis confirmed a reduced bacterial load in the ACJ group over time. Immunohistochemistry showed enhanced recruitment of macrophages and neutrophils in the ACJ-fed fish, particularly at Day 1 and Day 5 post-infection. Proteomic profiling of intestinal tissue identified 792 differentially abundant proteins (≥1.3-fold or ≤0.77-fold; P < 0.05), including those involved in phagosome formation, necroptosis, tight junction regulation, and arginine-proline metabolism. These findings demonstrate that dietary ACJ significantly enhances the innate immune response and confers increased resistance to A. salmonicida infection in zebrafish, supporting its potential as a functional feed ingredient in aquaculture.