Dietary supplementation of Patchouli oil increases the resistance against Streptococcus agalactiae infection in GIFT tilapia as revealed by transcriptome and 16s amplicon profiling

Abstract

Large-scale disease outbreaks that caused by Streptococcus agalactiae (SA) infection have dramatically affected tilapia production worldwide. Patchouli oil (PO) is a traditional Chinese herbal medicine in treating gastrointestinal symptoms and is considered to be a safe and efficient candidate to treat SA infection in tilapia. In this study, we first investigated the changes of intestinal microbiota and host responses in GIFT tilapia after a 28-day dietary supplementation of different concentrations of PO (basic diet, 5 μL PO/g diet, or 15 μL PO/g diet) and followed by SA infection using an integrative analysis of transcriptome and 16 S amplicon profiling. We observed that dietary supplementation of 5 μL PO/g diet improved food intake and growth in tilapia. Histopathological observation confirmed there were increased surface area of intestinal villi and generally decreased ROS as revealed by the MAD, GSH-PX, and T-SOD activities in the tilapia intestines in response to dietary PO supplementation. The intestinal microbial diversities and community structures were significantly affected, and the colonization of probiotics (e.g., Cetobacterium and clostridium_ sensu_stricto_1) in the mucosa was improved in the dietary PO groups. The relative abundance of Streptococcus (0.033%) in the 15 μL PO/g dietary group was much lower than that in the control group (basic diet; 0.86%). A large number of DEGs were enriched in the immune-related pathways, e.g., lysosomal lumen, MHC protein complex, and toll-like receptor 2 signaling pathway. Our findings suggested that dietary supplementation of PO enhanced intestinal physical barriers, increased the colonization of probiotic bacteria and improved intestinal immunity in tilapia. This provides novel knowledge on PO as a dietary supplement to improve intestinal health against SA invasion in tilapia.