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< 0.05).
3). Regulate immunity and improve disease resistance
Enterococcus faecalis can improve the immunity of aquatic animals and enhance their ability to resist pathogenic infection. The colonization of Enterococcus faecalis in the intestinal tract of aquatic animals can form a biofilm on the intestinal epithelial cells, protect the intestinal epithelial cells from harmful substances, and have an immune barrier effect. Enterococcus faecalis can stimulate immune cells to release immune factors, thereby improving the antioxidant capacity of aquatic animals. Huang Yanhua et al. added Enterococcus faecalis to the feed of one tilapia. The results showed that the activity of serum alkaline phosphatase, the ability of serum to resist superoxide anion free radicals and the ability to resist Aeromonas hydrophila infection were significantly improved. Enterococcus faecalis It has a significant effect on improving the immunity of one tilapia. Studies by Allameh et al. showed that feeding Enterococcus faecalis can significantly increase the antibody level of silver spiny barb during Aeromonas hydrophila infection, enhance the level of humoral immune response, and thus improve the survival rate. Urie et al. added Enterococcus faecalis to rainbow trout feed, which significantly increased its hematocrit, phagocytic index, phagocytic activity, and mucus production. Satoh studies have shown that the addition of inactivated Enterococcus faecalis to the feed enhances the immunity of rainbow trout and significantly reduces its mortality from A. salmonicida infection.
4). Improve aquaculture water environment
Environmental pollution of aquaculture water has become one of the prominent problems facing the aquaculture industry today. High-density seedlings and large-scale feeding of artificial compound feeds are two notable features of the current intensive aquaculture model. According to reports, 10% to 20% of the feed put in is not eaten by the farmed animals, but dispersed in the water environment; only about 20% to 25% of the feed nitrogen that is ingested is used for growth, and the remaining 75% to 80%. Excreted into water bodies in the form of feces and metabolites. Coupled with a large amount of fertilization, eutrophic factors such as residual bait, aquatic excrement and corpses, various organic and inorganic fertilizers cannot be cleaned up in time, resulting in imbalanced water ecological balance, ammonia nitrogen, nitrite, hydrogen sulfide and other harmful substances exceeding the standard, and a large number of harmful microorganisms. Growth, the growth of phytoplankton is inhibited and the dissolved oxygen is reduced. Under environmental stress, the growth of aquatic animals is inhibited and even causes diseases, which has caused great losses to aquaculture production. Beneficial microorganisms such as Enterococcus faecalis can decompose a large amount of residual bait accumulated at the bottom of aquaculture ponds into small molecules, which can be decomposed into carbon dioxide, nitrate, etc. The concentration of nitrates and sulfides is reduced, and phytoplankton can absorb and utilize the inorganic substances produced during photosynthesis, which can purify the water while increasing the dissolved oxygen in the pond, restore the aquaculture water environment and maintain the balance of the ecosystem.
3. Application of Enterococcus faecalis in aquaculture
1). Use as feed additive
The use of Enterococcus faecalis as a feed additive can adjust the balance of intestinal flora of aquatic animals, improve feed utilization, enhance immunity, and improve breeding efficiency. Huang Wang et al. added Enterococcus faecalis to the feed of Gift tilapia, and the results showed that the average tail weight (FBW), weight gain rate (WGR), specific growth rate (SGR) and average tail food intake (FI) of tilapia ) were significantly increased, the crude protein content and crude fat content of the whole fish were significantly higher than those of the control group, and the dry matter, protein and fat deposition rates were significantly higher than those of the control group. Zhou Xiaobo et al. compared the feeding effects of Lactobacillus acidophilus, Lactobacillus plantarum, Lactobacillus pentosus, Lactobacillus rhamnosus and Enterococcus faecalis on tilapia oneni, and the results showed that the effect of Enterococcus faecalis in tilapia The application effect is good. Adding Enterococcus faecalis to the feed can promote the growth of tilapia, improve feed utilization, reduce serum cholesterol and triglyceride content and alanine aminotransferase activity, increase the number of intestinal lactic acid bacteria, and improve the intestinal microenvironment. Adding Enterococcus faecalis to carp feed by Liu Cuiling can significantly reduce the bait coefficient (P<0.05); improve the apparent digestibility of crude fat (P<0.05); significantly increase the activities of protease and lipase in the hindgut (P<0.05) ; Serum alkaline phosphatase (AKP), alanine aminotransferase (GPT) and aspartate aminotransferase (GOT) and other non-specific immune-related enzyme activities were significantly increased (P < 0.05), indicating that the use of Enterococcus faecalis as a feed additive can improve carp immunity and promote its growth. When a strain of Enterococcus faecalis NRW-2 isolated from the intestines of gobies was added to the commercial diet of L. vannamei, the expression of immune genes in the midgut of P. vannamei was significantly enhanced, and the number of enteric Vibrio was significantly reduced. It was indicated that NRW-2 could significantly improve the pathogen resistance of Litopenaeus vannamei, and could be used as a feed additive. In practical application, factors such as aquatic animal species, growth stage and water environment conditions should be considered to determine the amount of Enterococcus faecalis added to the feed.
Take the use of Enterococcus faecalis 10 billion spores per gram of soluble powder as an example (please convert for other contents):
◆Poultry: 100g/ton feed
◆Livestock: 150g/ton feed
◆Aquaculture: 150g/ton feed
Mixed feed feeding:
◆Poultry: 100g/ton of feed, used throughout the whole farm.
◆Livestock: 100g/ton of feed is added, and it is used continuously for 10 to 15 days, and the effect of the whole process is better.
◆Aquaculture: 100g/ton of feed is added, and it is used continuously for 10 to 15 days, and the effect of the whole process is better.
Animal drinking water: add 0.3% to drinking water, use once a day
Breeding environment treatment: Dissolve 0.3g/square meter in an appropriate amount of water and sprinkle it evenly or directly, and use it every 10-15 days
Aquaculture water treatment: Sprinkle evenly with 50g/mu/m of water, and use it every 10-15 days.
In areas with severely deteriorating water quality, double use can be used every 5-7 days.
When used as a feed additive, probiotics not only have the effect of promoting growth and enhancing immunity, but also have a certain effect of improving the water environment. Tang Jufen et al. added a compound probiotic preparation containing Enterococcus faecalis, Lactobacillus acidophilus, Bacillus subtilis, Bacillus natto and Bacillus licheniformis to the compound feed of Litopenaeus vannamei for 30 days. The results showed that feeding compound probiotics In addition to improving the growth index and disease resistance of Litopenaeus vannamei, the preparation can maintain the pH value of the water body stable, and reduce the content of ammonia nitrogen (NH3-N) and nitrite nitrogen (NO2--N) in the water body. The environment has been effectively improved. The reason for the analysis may be that the probiotics are released into the water body with the residual bait or the probiotics are not colonized in the shrimp intestines and are discharged into the water body with the feces, where they grow and proliferate in a suitable environment, thereby playing a role in water quality regulation.
2). Use as water quality improver
The quality of aquaculture water environment is one of the key factors for the success or failure of aquaculture. Regular use of water quality improvers can significantly improve the aquaculture water environment, thereby promoting the healthy growth of farmed animals.
Enterococcus faecalis can be used as a water quality improver. Liu Yulin et al. applied Enterococcus faecalis as a water quality improver to grass carp aquaculture (once every 10 days, used throughout the whole process). Significantly reduce the concentration of NH3-N and NO2--N in the water, improve the pH and dissolved oxygen in the breeding environment, effectively improve the water quality and promote the growth of grass carp. Wang Yin et al. studied the effect of Enterococcus faecalis on NH3-N and NO2--N in water. The results showed that Enterococcus faecalis could effectively remove NH3-N and NO2-N in simulated sewage, and the removal rates within 5 days were 54.28 % and 100%. Zhang Qiuming and others regularly applied quicklime and micro-ecological preparations containing Enterococcus faecalis to the breeding ponds of yellow sand soft-shelled turtles, which could keep the water quality of the breeding ponds stable and improve the breeding efficiency.
4: Problems and Prospects
As a probiotic, Enterococcus faecalis has been widely used in aquaculture production, but there are still some problems in the production and use of Enterococcus faecalis products: 1) The bacteria are not resistant to high temperature and cannot tolerate compound feed production 2) The number of viable bacteria decreases rapidly during storage and use, and is susceptible to contamination by miscellaneous bacteria.
Therefore, further research is needed to screen the bacterial protection agent to improve the high temperature resistance of the preparation, so as to meet the requirements of the compound feed production process; the drying process and storage conditions of Enterococcus faecalis need to be further optimized to ensure that the bacteria can be dried and stored survival rate. With the in-depth research on Enterococcus faecalis, Enterococcus faecalis will play a more important role in the field of aquaculture and can promote the healthy development of the aquaculture industry.