The role and efficacy of Enterococcus faecalis and its application in aquaculture

The excessive pursuit of production in aquaculture often leads to high breeding density, which exceeds the carrying capacity of the water body, resulting in deterioration of the breeding environment, reduced immunity of aquatic animals, and increased difficulty in disease prevention and control. The unreasonable use of antibiotics, pesticides and other drugs The use of it will lead to problems such as enhanced resistance of pathogenic organisms and excessive drug residues. The above problems will hinder the sustainable development of aquaculture and even threaten human health. With the improvement of people's living standards and the enhancement of food safety awareness, higher requirements are put forward for the quality of aquatic products, which will promote the development of the aquaculture industry in the direction of healthy and ecological aquaculture.

Because of the characteristics of safety, high efficiency and no residue, microecological preparations are in line with the development trend of the aquaculture industry. They have received widespread attention and have been gradually promoted and applied in aquaculture. In ensuring the healthy and sustainable development of my country's aquaculture industry, reducing chemical reagents It plays an important role in reducing the drug residues in aquaculture aquatic products, and improving the quality and safety level of aquaculture aquatic products. At present, photosynthetic bacteria, bacillus, lactic acid bacteria and other microbial products have been widely used in aquaculture.

Enterococcus faecalis belongs to the Enterococcus family of lactic acid bacteria, Enterococcus genus, Enterococcus faecalis will produce a large amount of acid, etc. Enterococcus faecalis is paired with amino acids. It is one of the main bacterial groups in the human and animal intestinal tracts. It can convert some of the nitrogen-free extracts of carbohydrates into lactic acid for the body to use, and the secreted L-type lactic acid can be completely absorbed and utilized by the body. The "Catalogue of Feed Additives (2013)" defines Enterococcus faecalis as a strain that can be added to feed, which is more suitable for production and application than bifidobacteria with severe anaerobic culture and storage conditions. Enterococcus faecalis has broad application prospects in aquaculture as a microecological agent.

1: The biological characteristics of Enterococcus faecalis

Enterococcus faecalis is a gram-positive facultative anaerobic bacterium with a round or oval body, about 0.5-1.0 μm in diameter, which grows in a long chain in liquid medium, and a shorter one in solid medium. Double-chain or single short-chain arrangement, no flagella and spores around the cell body, no motility. Its nutrient requirements are low, it can grow on ordinary agar medium, and it grows well on medium containing serum. The colonies are large and smooth, flat and raised, opaque, gray-white, with intact edges, 1-2 mm in diameter, showing α or β. Hemolysis. It can grow at 10°C or 45°C, and can withstand 65°C for 30 minutes. It can grow in pH 9.6 and 6.5% NaCl broth. It can use arginine as energy, ferment glucose to produce acid but not gas, and does not ferment arabinose. Folic acid is not required for growth on simple media. The catalase test, nitrate reduction test, and contact enzyme test were all negative.

2: The main effect of Enterococcus faecalis in aquaculture

1.. Maintain the microecological balance of the digestive tract

Enterococcus faecalis can tolerate low pH, and has high tolerance to gastric juice, intestinal juice, and bile salts. Enterococcus faecalis can proliferate in large quantities after entering the intestinal tract, inhibit the growth of harmful microorganisms, regulate the intestinal microecological balance, and reduce the occurrence of intestinal diseases. The organic acids such as lactic acid, acetic acid and isobutyric acid produced during the growth and reproduction of Enterococcus faecalis can adjust the pH value of the intestinal tract, thereby inhibiting the growth of harmful microorganisms. In addition, E. faecalis can produce bacteriostatic metabolites, such as bacteriocins. Bacteriocins can specifically bind to receptors on the surface of sensitive cells, form ion channels, cause ion leakage, affect the synthesis of ATP and the transport of specific substances, inhibit the synthesis of macromolecular substances such as proteins and DNA, and cause cell death, thereby acting as a bacteriostatic agent. bactericidal effect. Studies have shown that Enterococcus faecalis has a good inhibitory effect on pathogens such as Aeromonas hydrophila, Pseudomonas aeruginosa, Shewanella spoilage, Escherichia coli, Staphylococcus aureus and Salmonella.

2., nutrition, promote growth

The L-type lactic acid secreted by Enterococcus faecalis after intestinal colonization can enhance the digestion and absorption capacity of the intestine; Enterococcus faecalis can increase the activities of digestive enzymes such as protease, amylase, lipase and cellulase in the digestive tract of aquatic animals. It can promote the decomposition of protein, fat and complex carbohydrates in the feed, and the generated monomers and energy supply the growth and development of the body, thereby improving the digestion and absorption rate of the feed and promoting the growth of aquatic animals; Enterococcus faecalis in the process of growth and reproduction It will also produce vitamins, amino acids, growth-promoting factors and other nutrients to promote the absorption of iron, calcium, zinc and other mineral elements to supplement the body's nutritional elements; in addition, Enterococcus faecalis can soften the fiber in the feed and improve the feed quality Conversion rate. Sha Yujie et al. added Enterococcus faecalis to the diet of Penaeus vannamei for 4 weeks, and the results showed that feeding Enterococcus faecalis could significantly increase the amylase and lipase activities in the intestine and hepatopancreas of Penaeus vannamei (P

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