Figure 1: The mechanism by which the inflammatory intestine drives the proliferation of Enterobacter (MY Zeng et al 2016)

1. Superoxide anion (O2-) and nitric oxide (NO) react to produce nitrate (NO3-), enterobacteria use nitrate to breathe and grow and proliferate; 2. The higher oxygen level in the inflamed intestine leads to the proliferation of enterobacteria, At the same time inhibit the growth of obligate anaerobes, Bacteroides and Clostridium; 3. Phospholipids in dead epithelial cells are decomposed to generate ethanolamine, which is converted into ammonia, which can be used for tricarboxylic acid cycle, glyoxylic acid cycle and lipid biosynthesis, to provide carbon source and nitrogen source for enterobacteria; 4. Goblet cells secrete MUC2 in the inflammatory intestines, enterobacteriaceae can use the sialic acid in MUC2 to synthesize bacterial capsules and lipo-oligosaccharides; 5. Bacteria released by Escherichia coli siderophore intestinal actin inhibits neutrophil myeloperoxidase; 6. Enterobacter that can express Collb releases Collb, forms pores in bacteria sensitive to Collb, destroys the synthesis of cell walls, and kills those sensitive to Collb Bacteria.

1. Anaerobic respiration

Enterobacter is a facultative anaerobic bacteria, which can adjust its own metabolism according to the different oxygen content in the intestines, and switch between aerobic respiration and anaerobic respiration at will. Under inflammatory conditions, reactive oxygen free radicals and reactive nitrogen free radicals in the intestinal cavity increase. When reactive oxygen free radicals react with nitric oxide to form peroxynitrite, they can quickly be converted into nitrate, The nitrate-rich tissue environment promotes the growth of enterobacteria such as E. coli through nitrate respiration.

In addition, reactive oxygen free radicals and reactive nitrogen free radicals can oxidize sulfides, such as methionine, tertiary amines, and trimethylamine (TMA) to produce S-oxides and N-oxides. These products can be used as electrons receptors for anaerobic respiration, which promote the growth and proliferation of Salmonella in the inflamed intestinal tract. Neutrophils that migrate into the intestinal lumen during inflammation produce reactive oxygen free radicals, which convert endogenous sulfides (thiosulfate) into electron acceptors (tetrathionate), and further breathe through tetrasulfate to promote the rapid proliferation of Salmonella in the inflamed intestine (Figure 2).

Figure 2. Tetrasulfate respiration (Andreas J.B, et al 2016)

2. Aerobic respiration

The higher blood flow and hemoglobin in the environment of the inflamed intestine are thought to cause an aerobic microenvironment in the intestinal lumen, which will lead to the rapid expansion of facultative anaerobes, such as enterobacteria, and inhibit obligate anaerobes, such as the growth of lactic acid bacteria and cellulolytic bacteria.

A 2016 study by Rivera-Chavez, F showed that when clostridia was treated with streptomycin, epithelial oxidation increased, leading to aerobic growth and expansion of Salmonella in the intestinal lumen.

3. Nutritional changes

Nutrition has a profound effect on the composition of gut microbes. In the inflammatory intestine, the mucosal layer of intestinal epithelial cells will increase the content of phospholipids due to the inflammatory response and the shedding of dead epithelial cells, which can be used as carbon and nitrogen sources by a variety of pathogens such as Salmonella and Pseudomonas, further promoting the proliferation of such bacteria.

Inflammation of the intestinal tract induces a decline in the diversity of intestinal microbes, and the decline in flora diversity makes the polysaccharide components of the intestinal mucosal layer used to protect intestinal epithelial cells more easily utilized by pathogenic microorganisms. The mucosal layer polysaccharides are degraded by symbiotic bacteria to release sugars, such as trehalose, galactose, and mannose, which can provide growth energy for pathogenic microorganisms (Figure 3).

Figure 3. Polysaccharides in the mucosal layer of the inflamed intestine are broken down to provide nutrition for pathogenic microorganisms (Andreas J.B et al 2016)

4. Mucin Utilization

The mucus layer covering the intestinal epithelium is the host's first line of defense against food or potentially invading pathogens in the lumen of the digestive tract. Increased mucin secretion is one of the signs of intestinal inflammation caused by harmful bacteria infection, and may be a mechanism that promotes the removal of pathogens and maintains the integrity of the mucus layer.

Sialic acid is one of the main carbohydrates in mucin, which can be used by Escherichia coli to synthesize bacterial capsules and lipo-oligosaccharides8. A 2015 study by Huang, Y.L and others reported that after DSS (Dextrose Sodium Sulfate) induced colon injury and inflammation, the content of sialic acid in the intestine increased, and Escherichia coli proliferated in large numbers.

Ⅱ. Changes of inflammatory reaction in piglets before and after weaning

Figure 4. Changes of various inflammatory cytokines with post-weaning diet (S. Pie, 2004)

Inflammation in the intestine arises from various conditions such as stress, harmful bacteria infection, body damage, antibiotic treatment, etc. However, the changes in the intestinal flora and intestinal morphology caused by inflammation are consistent, and usually promote the proliferation of harmful bacteria such as enterobacteria and decrease the expression of tight junctions in the intestine. so reducing inflammation will be one of the auxiliary means to improve intestinal health, and we should also consider it in our thinking of replacing antibiotics.

3. Measures to control intestinal inflammation

In the past, we extensively used antibiotics to inhibit bacteria and sterilization, and inhibit inflammation. However, the ban of antibiotics regulations require us to make a series of changes to make up for the lack of antibiotics and control inflammation. In addition to the management measures, the factors that can affect the inflammatory response in the feed include the following aspects:

1. Dietary fiber level

The fiber in the diet can be used by cellulolytic bacteria in the hindgut to produce short-chain fatty acids, such as propionic acid and butyric acid, which can reduce the levels of pro-inflammatory factors such as TNF-α and IL-6 in the intestine. Cellulolytic bacteria are strictly anaerobic bacteria, while yeast, especially S.boulardii® yeast, can quickly consume oxygen in the intestines and promote cellulolytic bacteria to ferment fibers to produce short-chain fatty acids, thereby reducing inflammation.

French pig farming expert Mr. Pierre suggested using soluble fiber and insoluble fiber to control and adjust the fiber level in the formula, and then make more targeted formula trimming for pigs of different stages and breeds.

2. Probiotics

Take S.boulardii® for example, as a unique special yeast probiotic, it can quickly consume intestinal oxygen, create a low-oxygen microenvironment, neutralize clostridial toxins, hydrolyze phosphonate polysaccharides, and reduce inflammation. After inflammation occurs, S.boulardii® inhibits the occurrence of excessive inflammation by regulating the type differentiation, function and migration of dendritic cells. Its metabolites have the ability to interfere with the integration of inflammatory nuclear transcription factors and regulate the activity of mitogen-activated protein kinases, which can significantly reduce the secretion of pro-inflammatory interleukins, such as IL-8, IL-6 and TNF-α, and increase the concentration of anti-inflammatory IL-10.

This mechanism has been successively verified in subsequent experiments. The 2009 results of Lessard showed that when piglets were infected with E. coli, whether it was the blank control group or the antibiotic treatment group, the intestinal secretion of the pro-inflammatory factor IL-8 was significantly increased. But the S.boulardii® group significantly inhibited the secretion of IL-8 during bacterial infections. Collier (2010) also observed that S.boulardii® significantly inhibited the level of pro-inflammatory IL-1β under artificially induced LPS poisoning conditions and reduced pig mortality (Figure 5).

Figure 5. S.boulardii® reduces piglet mortality after LPS challenge (Collier et al. 2010)

3. Plant extracts

Plant extracts include a variety of substances, such as phenols, aldehydes, and polyphenols. Polyphenols include tannins, flavonoids, and isoflavones, some of which are the main components of plant essential oils. In vivo and in vitro experiments have shown that certain polyphenols can improve health by improving intestinal tight junctions, reducing inflammation, and resisting oxidative stress (Figure 6).

4. Oxidation and antioxidant balance

Oxidative stress is not only the result of inflammation, but also one of the causes of inflammation. Since the excess free radicals caused by inflammation cannot be completely eliminate by the inherent antioxidants in the body, we must supplement them with additional antioxidants. Recent studies have shown that in addition to eliminating oxygen free radicals, antioxidants may also act by activating the antioxidant system in the body. Compared with severe clinical manifestations such as diarrhea, subclinical symptoms of milder oxidative stress are not easy to see, such as low feed intake. The use of effective antioxidant tools, such as the combination of VE, yeast selenium and polyphenols, can increase feed intake and improve production performance. 

Summary We can prevent and reduce the occurrence of inflammation through many means, and change the inflammatory intestinal environment to maintain the stability of the intestinal flora and the health of the host, and we believe that whether it is to directly inhibit inflammation or change the internal inflammation environment , S.boulardii® is one of our good choices, no antibiotics in feed, we have been working hard!