The development of green pollution-free feed additives is an important research direction of the feed industry in the 21st century. Feed microbiological agents are the main way to achieve this goal. This article focuses on the development of the lactic acid bacteria microbial agents, the mechanism of action, and ways to improve the application effect. The prospects for the safety and application prospects of lactic acid bacteria microorganisms are discussed. For the remaining problems such as antibiotics, hormones and stimulants, and threats to human health, scientists have put the research direction of animal drug additives into growth promotion and health care. The effect of feeding probiotics. Microecological preparations refer to the physiologically active products and their metabolites that regulate ecological disorders, maintain microecological balance, increase the health level of hosts (people, animals and plants), or enhance their health, and promote these physiological bacteria under the guidance of microecological theory. Group growth and reproduction of biological products. Development of Feeding Microbial Agents Feeding microorganisms must be biologically and genetically stable and safe. Therefore, they must be subjected to stringent pathological and toxicological tests before they are applied, which proves to be non-toxic, harmless, and non-drug resistant. Can use it. At present, there are several types of microorganisms that are commonly used, such as lactic acid bacteria, bacillus, bakelite, actinomycetes, light and bacteria. The FDA (1989) stipulates that there are more than 40 kinds of microorganisms allowed to be fed, and nearly 30 are lactic acid bacteria. China's Ministry of Agriculture in 1994 approved the use of microbial species: Bacillus cereus, Bacillus subtilis, Streptococcus faecalis, Bifidobacterium, Lactobacillus, Streptococcus lactis, etc. Most of them are also lactic acid bacteria. This article will take the lactic acid bacteria microbiological agent as a representative, preliminarily explore the microbial mechanism of action and its development and utilization. 2 Composition and Distribution of Lactic Acid Bacteria Lactic acid bacteria (LAB, Lactic Acid Bacteria) are a group of bacteria that can produce large quantities of lactic acid from fermentable carbohydrates (mainly glucose). At present, at least bacteria of this class have been found in taxonomy. Including 18 genera, mainly including: Lactobacillus, Bifidobacterium, Streptococcus, Leuconostoc, Enterococcus, Lactococcus , Carnobacterium, Atopobium, Pediococcus, Aerococcus, Vagococcus, Listeria, Sporolactobacillus ( Sporolactobacilus), a few species in Bacillus, Brochothrix, Erysipelothrix, Gemella, and Saccharococcus (Yang Jiebin et al., 1996) . The vast majority of lactic acid bacteria are anaerobic or facultative anaerobic chemolithotrophs, Gram positive. Growth and reproduction in anaerobic or slightly aerobic, mineral and organic nutrient rich slightly acidic environment. Sewage, fermentation production (such as silage, beer, kimchi, soy sauce, yogurt, cheese) culture, animal digestive tract and other high levels of lactic acid bacteria. The lactic acid bacteria in the stomach of the calf and the upper intestine are predominant. Lactobacillus lactis and fermented lactobacillus are separated from the calf-fed calf's gastric juice, while in the rumen of the calf, mainly is Lactobacillus acidophilus. Lactobacillus fermentum is adhered to the columnar epithelium. The main lactobacillus of the cell. 3. The mechanism of action of lactic acid bacteria Lactic acid bacteria have health and therapeutic effects on humans and animals. This point, both at home and abroad have a large number of feeding and clinical trials. Baird (1977) used lactobacilli to feed weaned pigs and grow-finish pigs. Tests have shown that both increase daily gain and improve feed conversion; Lidbeck et al. (1992) confirmed that Lactobacillus can prevent radiation-induced diarrhea. Cai Huiyi et al. (1993) have statistics on the effects of the use of prebiotics, including reports that lactic acid bacteria probiotics are fed to pigs, 7 examples can increase daily weight gain, an average increase of 7.67%, and 6 examples increase feed conversion rate, an average increase of 5.4%. In the report on broilers fed, 5 examples showed that the daily gain was increased by an average of 7.32%, and 5 examples showed that the feed utilization rate was increased to an average of 9.5. The average daily growth of Lactobacillus was increased when fed with fattened cattle (fed). The weight gain was increased by 13.2%, the feed conversion rate was increased by 6.3%, and the incidence rate decreased by 27.7%. Gallagher et al. (1974) showed that the consumption of lactose by people who consume yogurt is higher than that of milk containing the same lactose concentration, thereby reducing the symptoms of lactose intolerance. In addition, the anti-cancer effects of lactic acid bacteria have also been reported. Lactic acid bacteria have a significant effect in practical applications. In the past two years, more research work has focused on the role of lactic acid bacteria in exerting these functions. There are many reports. In summary, the main mechanism of action is as follows: 1) Provide nutrients and promote growth of the body. 2) Improve the micro-ecological environment and clean up intestinal toxic substances. 3) Regulate the digestive immune system. 3.1 Providing nutrients to promote body growth Lactic acid bacteria, if they can normally exert their metabolic activity in the body, can directly supply the host with essential amino acids (such as lysine and methionine) and various vitamins (vitamin B and K, H, etc.) can also increase the biological activity of mineral elements, and in turn provide the host with essential nutrients, enhance the animal's nutrient metabolism, and directly promote its growth. Hamad (1979) showed that the nutritional value of wheat, rice, corn and other cereals was greatly increased. Bi Decheng et al. (1988) used Lactobacillus bulgaricus and Streptococcus thermophilus to ferment corn and wheat flour and found that the lysine content increased respectively. In 72% and 85%, methionine increased by 40% and 46%, thiamine (VB1) and riboflavin (VB2) increased, free nitrogen increased 1.6-fold and 1.4-fold, and free iron increased by 1.3-fold. At 9-fold, free calcium increased by 1.5 and 1.2 times, and the overall nutritional value improved significantly. In addition, the acidic metabolites produced by lactic acid bacteria make the intestinal environment acidic, and the general pH of digestive enzymes is partially acidic (amylase 6.5, glucoamylase 4.4), which is conducive to the digestion and absorption of nutrients, the production of organic acids. It can also strengthen the intestinal peristalsis and secretion, but also promote digestion and absorption of nutrients (tension, etc., 2000). 3.2 Improve micro-environment The entire digestive tract of animals is normally parasitized with a large number of microorganisms. In terms of their functions, they can be divided into three categories: 1) Symbiotic types, mainly facultative anaerobic bacteria, in the ecological balance, their functions of microsynthetic and protein synthesis, digestion and absorption, biological resistance and immunity, etc. Good for the host. 2) Type of pathogenicity. Normally, the number of pathogenicity is small. Parasitizing in the normal site will not cause the host to become ill. If it is out of control, it will lead to host adverse reactions. 3) The intermediate type, which has both physiological and pathogenic effects, will increase the number of rot biomass, increase toxins, and promote host aging (Kang White, 1988). The balance of microbiota is very important to the health of the organism, and lactic acid bacteria can regulate this microecological balance and protect the normal physiological state of the host. During the growth and metabolism of lactic acid bacteria, there will be some substances with anti-microbial activity, such as organic acids, hydrogen peroxide, and carbon dioxide, all exhibiting antibacterial activity in vitro. Many lactic acid bacteria can produce bacteriocins, such as nisin, lactobacilli, and phletocin. Studies have shown that these substances play an important role in the inhibition of pathogenic bacteria. Adhesion capacity is generally considered to be an important virulence factor for pathogens (Finary et al., 1997). Adhesion to the intestinal mucosa is a prerequisite for pathogen colonization and clinical symptoms. Lactic acid bacteria can prevent pathogens from attaching to the surface of intestinal epithelial cells and colonize and invade intestinal cells. Some people call this mechanism "adhesion resistance." The composition of intestinal chemical substances is also an important influencing factor in the micro-ecological environment. Toxicants, sulfides, quinones, and phenols are substances that have irritating and toxic effects on the intestinal tract, and are signs of enhanced activity of intestinal spoilage bacteria. Bifidobacteria can prevent the decarboxylation of amino acids by pathogenic bacteria, reduce the concentration of ammonia in the contents of the intestine, effectively reduce the synthesis of toxic amines, and improve the intestinal environment. 3.3 Regulation of Immune System Function Lactic acid bacteria preparations can enhance immunity, manifested in two aspects: First, affect non-specific immune response, enhance the activity of mononuclear phagocytic cells (monocytes and macrophages), polymorphonuclear leukocytes, stimulation The secretion of reactive oxygen species, lysosomal enzymes, and monokaryotic factors; the second is to stimulate specific immune responses, such as strengthening the mucosal surface and serum IgA and IgM, IgG levels to enhance humoral immunity, and promote the proliferation of T and B lymphocytes. cellular immunity. Schiffrin et al. (1994) found that L.johnsonnii Lj1 and B. lactis Bb12 can enhance phagocytic phagocytosis of E. coli in vitro; Streptococcus and Salmonella can be used together. The effect of immune adjuvants significantly increases the serum IgA content. Gill (1998) listed some of the lactic acid bacteria tests conducted on any animal from 1985 to 1995, and the results all showed positive results. The stimulatory mechanism of lactic acid bacteria on the immune system is still under further study. Ouwehand et al. (1999) proposed a possible approach to the effects of probiotics (including lactic acid bacteria) on immune stimulation: antigenic substances pass through the follicle epithelium in lymphoid nodes, and there are two pathways: First, microbial metabolites or debris as Small-molecule antigens pass directly through common epithelial cells or through tight junctions between epithelial cells; second, the microbial cells themselves are transmitted by pinocytosis by M-Cells to M-Cell cysts. The macrophages, etc., enter the lymphoid tissue, or are processed by the antigen-presenting cells or directly delivered to lymphocytes to generate a corresponding immune response. 4. Application and Development of Lactic Acid Bacteria - 4.1 Principles for Selecting Strains to Be Screened Due to the deep understanding of the metabolism and genetic characteristics of Lactobacillus as well as the understanding of its mechanism, there are a large number of clinical trials that prove its feasibility as a supplement for health care and feed additives. Sex, people have widely accepted such health products as lactic acid bacteria. Currently, there are several major categories of livestock and poultry probiotics sold on the market, including Bacillus, Lactobacilli, Bifidobacteria, and yeast cultures. The screening of strains and the determination of their activity are key issues in the study of probiotics and determine the use of microecological agents. Fuller (1989) and Ouwehand et al. (1999) proposed the principle of selection for strains of probiotics. In summary, the main points are as follows: 1) The source of the original host. There is a specific mutual selection relationship between host and gut bacteria. The strains in the sow are more likely to colonize piglets, so the source of the strain should be the same as the object of use. Only in this way can the specific effects of probiotics be enhanced. 2) Colonization and adhesion. The adhesion of probiotics on the intestinal wall is an important step in the colonization process of probiotics, and it is the premise for mass reproduction to become a dominant population. Therefore, the strength of adhesion is one of the important criteria for screening probiotic strains. 3) Viability in acidic and highly bile salt environments. Oral administration is the main way for probiotics to enter the intestine, so probiotics must be subjected to hydrochloric acid in the stomach and high concentrations of bile salts in the small intestine before entering the large intestine. Only strains with high survival rates in hydrochloric acid and bile salts can work. 4) Specific physiological functions. All kinds of probiotics have their specific physiological functions, such as Lactobacillus acidophilus has a strong regulatory effect on the host's immune system, while Lactobacillus rhamnosus has a strong inhibitory effect on E. coli. Only in-depth study and understanding of the biological characteristics of each strain can be targeted to design a micro-ecological agent with a specific growth effect according to different situations. 5) The number of stable viable cells in the product. The number of live bacteria in the microecological preparation is the key to its function. Therefore, the application of live bacterial preparation requires that the unit product reach a certain number of viable cells in order to meet the effective therapeutic dose standard. 4.2 Research directions that can improve the application effect of lactic acid bacteria In order to make better use of the effect of lactic acid bacteria, many researches have been done in recent years on microbial strains, production processes, and product forms. There are mainly the following aspects: 1) Compatibility of multiple strains. Tests have shown that the combined use of Lactobacilli and Bifidobacteria can increase their effectiveness. Strict anaerobic strains co-cultured with non-strict anaerobic strains can increase the yield and survival rate of anaerobic bacteria, which is beneficial to the effectiveness of each strain. 2) Increase the number of lactic acid bacteria in the finished product. Trace elements (Fe, Cu, Zn, Se, Mo, etc.) are added. Amino acids (Arg, Tyr, Pro, Phe, etc.) and B vitamins, etc. required for cell growth are placed in the medium to promote the growth of the strain and can be prolonged. Its survival time in the finished product (Tang et al., 1996). 3) Use a suitable carrier to allow the probiotic strain to successfully reach the desired location. It has been verified that yoghurt is an effective carrier of lactobacillus and bifidobacteria, which increases the survival rate during their entry into the intestine (Kailasapathy et al., 2000). 4) Composite use of probiotics and enzyme preparations, organic germanium, polyterpenes, and Chinese herbal medicines. Shi Chuanlin and others successively studied the application of enzyme-enriched probiotics in finishing pigs, sheep, meat rabbits, cattle, chickens, and other livestock and poultry. The results all had significant growth-promoting effects, reduced feed costs, and achieved significant economic benefits. . From the results of the study, the combination of lactic acid bacteria probiotics and other feed additives has achieved good results. 5. The safety issue of lactic acid bacteria micro-ecological preparations For live microorganisms used in feed and food, the potential pathogenicity, the possibility of drug-resistance gene transfer, and the uncontrollability of reproduction and variation all need attention. Adams (1999) reviewed the organism infections that may be caused by lactic acid bacteria: endocarditis, bacteremia, and other infections of the chest and digestive tract. The potential dangers of lactic acid bacteria mentioned above should be noticed. But more should see the more beneficial part of lactic acid bacteria. There is evidence that human infections caused by lactic acid bacteria are relatively rare except for enterococci. Therefore, scientists believe that using lactic acid bacteria after strict inspection under effective supervision and control can be considered safe. The items to be tested include: intrinsic properties, metabolites, toxicity, effects on the mucous membranes, and measurement reactions. Clinical assessment, epidemiological studies, etc. Dunne et al. (1999) also reminded the investigators that they should also be aware that each strain must be tested and cannot be guessed by similar strains; the strains and products must be rigorously identified before clinical trials; the results are independent The research institution confirms. Lactic acid bacteria micro-ecological preparations provide a new choice for feed, livestock and poultry breeding industry with high efficiency, harmlessness and pollution-free. Its production and development conforms to the current high-tech industrialization and environmental protection-oriented mainstream. It fully considers the characteristics of the animal flora itself and the relationship between the host and the environment. Scientific and rational use will surely become the leading factor in the feed additives of this century. product.
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