Dietary supplementation of Streptococcus faecalis benefits the feed utilization, antioxidant capability, innate immunity, and disease resistance of blunt snout bream (Megalobrama amblycephala)

Acanthopanax senticosus cultures fermented by Lactobacillus rhamnosus enhanced immune response through improvement of antioxidant activity and inflammation in crucian carp (Carassius auratus)

Lactic acid bacteria (LAB) have been recognized as safe microorganism that improve micro-flora disturbances and enhance immune response. A well-know traditional herbal medicine, Acanthopanax senticosus (As) was extensively utilized in aquaculture to improve growth performance and disease resistance. Particularly, the septicemia, skin wound and gastroenteritis caused by Aeromonas hydrophila threaten the health of aquatic animals and human. However, the effects of probiotic fermented with A. senticosus product on the immune regulation and pathogen prevention in fish remain unclear. Here, the aim of the present study was to elucidate whether the A. senticosus fermentation by Lactobacillus rhamnosus improve immune barrier function. The crucian carp were fed with basal diet supplemented with L. rhamnosus fermented A. senticosus cultures at 2 %, 4 %, 6 % and 8 % bacterial inoculum for 8 weeks. After trials, the weight gain rate (WGR), specific growth rate (SGR) were significantly increased, especially in LGG-6 group. The results confirmed that the level of the CAT, GSH-PX, SOD, lysozyme, and MDA was enhanced in fish received with probiotic fermented product. Moreover, the L. rhamnosus fermented A. senticosus cultures could trigger innate and adaptive immunity, including the up-regulation of the C3, C4, and IgM concentration. The results of qRT-PCR revealed that stronger mRNA transcription of IL-1β, IL-10, IFN-γ, TNF-α, and MyD88 genes in the liver, spleen, kidney, intestine and gills tissues of fish treated with probiotic fermented with A. senticosus product. After infected with A. hydrophila, the survival rate of the LGG-2 (40 %), LGG-4 (50 %), LGG-6 (60 %), LGG-8 (50 %) groups was higher than the control group. Meanwhile, the pathological damage of the liver, spleen, head-kidney, and intestine tissues of probiotic fermentation-fed fish could be alleviated after pathogen infection. Therefore, the present work indicated that L. rhamnosus fermented A. senticosus could be regard as a potential intestine-target therapy strategy to protecting fish from pathogenic bacteria infection.

Effects of ribonucleotide supplementation in modulating the growth of probiotic Bacillus subtilis and the synergistic benefits for improving the health performance of Asian seabass (Lates calcarifer)

In aquaculture, due to the requirements for high-density culture, the diseases caused by bacterial pathogens have become a serious issue. To solve this problem, we performed synbiotic application of RNA and Bacillus subtilis as a sustainable and eco-friendly approach to improve the health and immunity of Asian seabass (Lates calcarifer) during cultivation without using any harmful antibiotics or chemicals. Among various forms of nucleic acids, such as mononucleotides and DNA, RNA was found to be most effective in promoting the growth performance of probiotic B. subtilis in all the tested minimal medium conditions. Accordingly, we used the synbiotic combination of B. subtilis and RNA for Asian seabass cultivation. After feed supplementation for fourteen days, the fish that received the combination treatment exhibited a significant increase in innate cellular and humoral immune parameters, including phagocytic activity, phagocytic index, respiratory burst, serum lysozyme and bactericidal activities, as well as upregulated expression of immune-related genes, including HEPC1, A2M, C3, CC, CLEC, LYS, HSP70, and HSP90. Furthermore, significant increases were observed in the ileal villus height and goblet cell numbers in the intestinal villi in all fish treatment groups. The combination treatment did not cause histopathological abnormalities in the intestine and liver, suggesting that the synbiotic treatment is safe for use in fish. The treated Asian seabass also exhibited a significantly increased survival rate after Aeromonas hydrophila challenge. These results indicate that the synbiotic mixture of B. subtilis and RNA can be considered a beneficial feed additive and immunostimulant for Asian seabass cultivation.

Dietary supplementation of probiotics fermented Chinese herbal medicine Sanguisorba officinalis cultures enhanced immune response and disease resistance of crucian carp (Carassius auratus) against Aeromonas hydrophila

Aeromonas hydrophila, a Gram-negative bacterium, is one of the major pathogens causing bacterial sepsis in aquatic animals due to drug resistance and pathogenicity, which could cause high mortality and serious economic losses to the aquaculture. Sanguisorba officinalis (called DiYu in Chinese, DY) is well known as herbal medicine, which could inhibit the growth of pathogenic bacteria, hemostasis and regulate the immune response. Moreover, the active ingredients in DY could remarkably reduce drug resistance. In this study, we investigated the effects of probiotic fermentation cultures on A. hydrophila through in vitro and in vivo experiments. Three lactic acid bacteria, including Lactobacillus rhamnosus (LGG), Lactobacillus casei (LC) and Lactobacillus plantarum (LP), were selected to ferment the Chinese herbal medicine DY. The assays of antagonism showed that all three fermented cultures could influence the ability of A. hydrophila growth, among which L. rhamnosus fermented DY cultures appeared to be the strongest inhibitory effect. In addition, the biofilm determination revealed that L. rhamnosus fermented DY cultures could significantly inhibit the biofilm formation of A. hydrophila compared to the other groups. Furthermore, protease, lecithinase and urease activities were found in the three fermentation cultures. Three probiotics fermented DY cultures were orally administration with crucian carp to evaluate the growth performance, immunological parameters and pathogen resistance. The results showed that the three fermentation cultures could promote the growth performance of crucian carp, and the immunoglobulins, antioxidant-related enzymes and immune-related genes were significantly enhanced. Besides, the results showed that crucian carp received L. rhamnosus (60.87%), L. casei (56.09%) and L. plantarum (41.46%) fermented DY cultures had higher survival rates compared with the control group after infection with A. hydrophila. Meanwhile, the pathological tissue results revealed that the probiotic fermented cultures could largely improve the tissues damage caused by the pathogenic bacteria. In conclusion, this study proved that the fermentation cultures of three probiotics could effectively inhibit the growth of A. hydrophila, regulate the level of immune response and improve the survival rate against A. hydrophila in crucian carp. The present data suggest that probiotic fermented Sanguisorba officinalis act as a potential gut-targeted therapy regimens to protecting fish from pathogenic bacteria infection.

Effects of Dietary Enterococcus faecalis YFI-G720 on the Growth, Immunity, Serum Biochemical, Intestinal Morphology, Intestinal Microbiota, and Disease Resistance of Crucian Carp (Carassius auratus)

Diseases of crucian carp (Carassius auratus) are closely related to intestinal parameters. Enterococcus faecalis has strong colonization ability in the intestinal tract, and produces natural antibiotics, bacteriocin, and other bacteriostatic substances, which can effectively inhibit some pathogenic bacteria and improve the intestinal microenvironment. This study aimed to assess the effects of E. faecalis YFI-G720 which was isolated from the intestinal of crucian carp on the growth, immunity, intestinal health, and disease resistance of crucian carp. Fish (48.16 ± 0.55 g) were fed four diets, commercial diet or diet containing E. faecalis at 105 CFU/g (EF1), 106 CFU/g (EF2), or 107 CFU/g (EF3) for 28 days. The results showed that supplementation of E. faecalis significantly improved the weight gain ratio (WGR) and the specific growth rate (SGR) compared with control group (p < 0.05). Intestinal mucosal epithelial cells in EF2 were intact and normal, but there was obvious vacuolation in CG. Compared with CG, serum C3 and IgM in EF2 were significantly increased at the end of the experiment (p < 0.05), and serum alkaline phosphatase was significantly higher in all experimental groups (p < 0.05). Among studied immune-related genes, expression was detected by qPCR, C3, IgM, and IL-1βwere upregulated in all experimental groups to varying degrees from 14 days, with highest expression in EF2 at 28 days. Intestinal microbiota structure analyzed through high-throughput sequencing, and the results showed that the relative abundance of Aeromonas and Acinetobacter decreased while Cetobacterium increased in all experimental groups, with the greatest changes in EF2. Challenge tests showed that fish fed E. faecalis were more resistant to Aeromonas veronii (p < 0.05). In conclusion, dietary E. faecalis YFI-G720 at 106 CFU/g can improve the health status, immune parameters, intestinal microbiota composition, and disease resistance of crucian carp.

Regulation of growth, intestinal microflora composition and expression of immune-related genes by dietary supplementation of Streptococcus faecalis in blunt snout bream (Megalobrama amblycephala)

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.