Effect of quorum quenching enzyme YtnP on immune response and intestinal microbiota in Aeromonas hydrophila-infected grass carp (Ctenopharyngodon idella).

Aeromonas hydrophila induces tissue swelling, necrosis, ulcers, and hemorrhagic septicemia in grass carp, causing significant economic losses. Quorum sensing, a communication mechanism among microorganisms, plays a key role in microbial ecological competition and dynamic equilibrium. Quorum quenching has emerged as a hot spot in anti-bacterial infection research. In this study, grass carp (n = 75 per group) were intraperitoneally injected with A. hydrophila and the quorum quenching enzyme YtnP. The expression levels of immune-related genes were assessed by qPCR. The intestinal microbiota was sequenced using the Illumina HiSeq 6,000 platform, with subsequent bioinformatics analysis. Co-treatment with YtnP significantly improved the survival rate of grass carp infected with A. hydrophila, increasing the survival rate from 57% in the AH group (A. hydrophila-infected only) to 87% in the AY group (co-administration of A. hydrophila and YtnP). Analysis of immune-related gene expression showed that the AH group exhibited early upregulation of the pro-inflammatory IL-1β and TNF-α, whereas the AY group showed increased expression of IFN-γ1, IL-6, IL-15, and IL-10, suggesting that YtnP contributed to immune regulation. Microbiota analysis revealed A. hydrophila infection caused dysbiosis, with a significant increase in the relative abundance of Proteobacteria and significant decreases in Fusobacteria and Actinobacteria. YtnP treatment significantly restored the abundance of Fusobacteria and Actinobacteria and altered predicted metabolic pathways related to aromatic compound metabolism and enterobactin biosynthesis, suggesting a potential role in modulating intestinal microbial community structure during A. hydrophila infection. By blocking bacterial virulence signal transmission and restructuring the intestinal microbiota toward probiotic enrichment, YtnP enhanced the host's innate immune response to A. hydrophila and restored host-microbiota homeostasis. This study establishes YtnP as a potential antimicrobial agent for sustainable aquaculture and provides a theoretical foundation for the quorum quenching-based immune-microbiota interaction mechanism in fish.