A 10-week feeding trial was performed to investigate the effects of Streptococcus faecalis on the growth, intestinal microflora composition and expression of immune-related genes of blunt snout bream (Megalobrama amblycephala). Fish (46.32 ± 0.09 g) were fed four experimental diets containing 0 cfu/g (SF0, control), 1 × 10⁵ cfu/g (SF1), 1 × 10⁶ cfu/g (SF2) and 1 × 10⁷ cfu/g (SF3) of S. faecalis, respectively. Results showed that daily growth index (DGI), feed efficiency ratio (FER), plasma glucose level, plasma contents of total protein and albumin as well as intestinal serous layer (SL), muscular layer (ML), submucous layer (SML), villi thickness (VT) and lamina propria (LP) were all no significant difference among all the treatments, whereas their (except plasma albumin content and intestinal ML) relatively high values were found in the SF2 group. Meanwhile, the intake of the SF2 diets significantly increased plasma globulin content and intestinal digestive enzymes activities, the opposite was true for the activities of plasma aspartate aminotransferase (AST) and alanine transaminase (ALT). In addition, the analysis of the intestinal microbiota showed that fish fed the SF2 diet have the highest values of intestinal alpha diversity and intestinal abundances of Actinobacteria, Chlamydiae, Firmicutes, Planctomycetes, Verrucomicrobia, Clostridium and Synechococcus, while the opposite was true for intestinal abundances of Acinetobacter, Anoxybacillus, Flavobacterium, Planctomyces, Plesiomonas, Pseudomonas, Staphylococcus and Clostridium perfringens. At the molecular level, the expression levels of tumour necrosis factor α (TNF α), interleukin 1β (IL 1β) and heat shock proteins 7 (HSP 70) in head kidney and spleen were all decreased significantly with the increasing S. faecalis levels up to 1 × 10⁶ cfu/g, and then they were increased with further increasing S. faecalis levels. Overall, dietary supplementation of S. faecalis at 1 × 10⁶ cfu/g could improve the intestinal health and innate immunity of blunt snout bream.

进行了为期10周的喂养试验，以研究粪便链球菌对钝嘴鲷（Megalobrama amblycephala）的生长，肠道菌群组成和免疫相关基因表达的影响。鱼（46.32±0.09 g）饲喂四种实验日粮，分别为0 cfu / g（SF0，对照），1×10 ⁵  cfu / g（SF1），1×10 ⁶  cfu / g（SF2）和1×10 ⁷  cfu / g（SF3）粪链球菌， 分别。结果显示每日生长指数（DGI），饲料效率比（FER），血浆葡萄糖水平，总蛋白和白蛋白的血浆含量以及肠浆层（SL），肌肉层（ML），粘膜下层（SML），绒毛厚度（VT）和固有层（LP）在所有治疗之间均无显着差异，而在SF2组中它们的值（血浆白蛋白含量和肠道ML除外）相对较高。同时，摄入SF2日粮显着增加了血浆球蛋白含量和肠道消化酶活性，血浆天冬氨酸转氨酶（AST）和丙氨酸转氨酶（ALT）的活性相反。此外，梭状芽孢杆菌和蓝细菌，而相反的是为肠道丰度真不动杆菌，Anoxybacillus，黄杆菌，浮霉状菌属，邻单胞菌，假单胞菌，金黄色葡萄球菌和产气荚膜梭菌。在分子水平上，随着粪肠球菌水平的升高，肿瘤坏死因子α（TNFα），白介素1β（IL1β）和热休克蛋白7（HSP 70）的表达水平均显着降低。到1×10 ⁶  cfu / g，然后随着进一步增加而增加粪链球菌水平。总体而言，粪便链球菌的饮食补充量为1×10 ⁶  cfu / g可以改善肠道健康和钝嘴鼻鲷的先天免疫力。