Effect of Enterococcus faecium as a Water and/or Feed Additive on the Gut Microbiota, Hematologic and Immunological Parameters, and Resistance Against Francisellosis and Streptococcosis in Nile Tilapia (Oreochromis niloticus).

Suelen Aparecida Suphoronski,Leonardo Mantovani Favero,Ulisses De Padua Pereira,Roberta Torres Chideroli,Henrique Momo Ziemniczak,Natália Amoroso Ferrari,Nelson Mauricio Lopera Barrero,Felipe Pinheiro De Souza,Daniela Dib Gonçalves

doi:10.3389/fmicb.2021.743957

Suelen Aparecida Suphoronski, Leonardo Mantovani Favero + Show 7 more

Open Access

https://doi.org/10.3389/fmicb.2021.743957

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Abstract

In the present study, we evaluated the effects of administering Enterococcus faecium in food and/or water on the hematological and immunological parameters, intestinal microbiota, resistance to bacterial diseases (streptococcosis and francisellosis) and growth of Nile tilapia. Before the in vivo experiment, probiotic bacteria isolated from Nile tilapia were selected via inhibition tests. Sequencing, annotation, and assembly of the complete genome of the selected bacteria as well as other tests were performed using bioinformatics tools. Three treatments were implemented: G1 (probiotic feeding), G2 (probiotic in water), and G3 (probiotic in food and water); and a negative control (NC) was also employed. Treatment lasted 38 days, and each group consisted of fish and two repetitions. The fish were divided and infected with Streptococcus agalactiae S13 (serotype Ib) and Francisella orientalis. The G1 group had a higher average final weight gain than the G2, G3, and NC groups. Further, a significant increase in the number of thrombocytes was observed in the groups administered probiotics in the diet (G1 and G3). A statistical difference was observed in the mortality of fish infected with S. agalactiae in the NC compared to the treated groups. Cetobacterium was the 43 most abundant genus in the intestinal microbiota of all groups, including the NC group. E. faecium increased the immunity of fish administered the treatment and decreased the mortality caused by S. agalactiae. As an autochtone probiotic, E. faecium does not interfere with the local ecosystem and thus has a great probiotic potential for Nile tilapia in Brazil.

Highlights

Fish farming is one of the largest aquaculture activity in the world, with Nile tilapia (Oreochromis niloticus) being a species of great importance [Food and Agriculture Organization (FAO), 2020]
The E. faecium antagonism against Staphylococcus spp. and the inhibition of supernatant of probiotic strain are demonstrated in Supplementary Figure 3
The use of probiotics in aquaculture is increasingly being considered as an eco-friendly approach to mitigate healthrelated problems

Summary

Introduction

Fish farming is one of the largest aquaculture activity in the world, with Nile tilapia (Oreochromis niloticus) being a species of great importance [Food and Agriculture Organization (FAO), 2020]. Brazil is estimated to lose 84 million dollars per year in freshwater fish farming owing to losses caused by diseases, with bacteriosis being the most important contributing disease (Tavares-Dias and Martins, 2017) Bacteriosis, such as streptococcosis and francicellosis, is known to cause high mortality rates in fish (Soto et al, 2009). Probiotics, either alone or combined with supplements, can elevate phagocytic, lysozyme, complement, respiratory burst activity, and the expression of various cytokines in fish (Wang et al, 2008, 2017; Ruiz et al, 2020) They stimulate the gut immune system of fish, with a marked increase in the number of Ig (+) cells and acidophilic granulocytes (Nayak, 2010)

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