Effects of Dietary Supplement of Probiotic Enterococcus faecium on Intestinal Microbiota and Barrier Structure, Immune Function, and Antioxidant Capacity of Soft-Shelled Turtle Pelodiscus sinensis

Abstract

Enterococcus faecium inhabits animal gastrointestinal tracts and has been demonstrated to benefit livestock and poultry, but its effects on soft-shelled turtles remain unexplored. The present work investigates the effects of probiotic E. faecium on intestinal microbiota and barrier structure, immune function, and antioxidant capacity of the soft-shelled turtle. Twenty-four juvenile Pelodiscus sinensis were divided into two groups: control (fed a basal diet) and treatment (fed a diet supplemented with E. faecium, 3.3 × 10⁸ CFU/g feed), over a period of 6 weeks. We found that E. faecium did not promote the growth of turtles at the present feeding level, but the treatment resulted in significant alterations in the intestinal microbial community structure, with increased abundance of Enterococcus, Romboutsia, and Clostridium_sensu_stricto_1, and a reduction in Aeromonas (p  < 0.05). E. faecium notably enhanced villus height/crypt depth, villus width, and villus density in the intestine. The treatment group exhibited a 1.50-fold increase in goblet cells count and a 1.18-fold higher in the muscular layer thickness compared to the control group. E. faecium also improved the immune function, with an increase in the ratio of plasma neutrophils and lymphocytes to the total number of leukocytes after feeding probiotics, and upregulation of the levels of toll-like receptor 4 (TLR 4), lysozyme, interleukin 1β (IL-1β), tumor necrosis factor α (TNF-α), and immunoglobulin A (IgA) in the intestine, as well as the level of hepatic immunoglobulin M (IgM). Additionally, E. faecium supplementation boosted antioxidant capabilities, including a significant increase in catalase (CAT) and glutathione peroxidase (GPx) activity and reduced glutathione (GSH) levels in the intestine and GSH levels in the spleen. Our study demonstrates the beneficial effects of supplemental E. faecium on the intestine and overall health of soft-shelled turtles, particularly in enhancing their immune function and antioxidant capacity.