Antibacterial activities of polyphosphates have been demonstrated in previous studies7. It has been reported that antibacterial activities of PGUC (polyphosphate derivative of guanidine and urea copolymer) against Gram-positive bacteria are higher than those against Gram-negative bacteria due to high adsorption of PUGC to the anionic surface of cell wall, causing damage to the cytoplasmic membrane17. In addition, in several experiments investigating antibacterial activities of different types of polyphosphates, some pathogenic bacteria were more sensitive to concentrations of polyphosphates, with lower concentrations of phosphates being less effective in inhibiting the growth of undesirable microorganisms, especially for short chain polyphosphates. Results of the P3 experimental group in the present study corroborate this finding of previous studies. There is a possibility that polyphosphates can isolate metal ions to stabilize, thus reducing the availability of nutrients to cells and making cells gradually become apoptotic18,7. In the presence of long-chain polyphosphate, cell envelopes (cell walls or cell membranes) of Staphylococcus aureus and Bacillus cereus are damaged. It is worth stating that 0.1% polyphosphate inhibits spore germination and growth, while high concentrations (1.0%) of polyphosphate can even kill spores. In addition, bactericidal and bacteriolytic effects of polyphosphate could be reversed or blocked by Ca2+ or Mg2+. Chelation of calcium and magnesium by long-chain polyphosphate increases with increasing pH. Chelation of metal ions participates in its antibacterial mechanism19,20. On the other hand, Gram-negative bacteria appear to be resistant to antibacterial properties of polyphosphate. High concentrations of polyphosphate could not even affect some Gram-negative bacteria21,22. It is noteworthy that Gram-positive bacteria have much higher requirements for Mg2+ than Gram-negative bacteria, which might be a contributing factor to the greater sensitivity of Gram-positive bacteria to polyphosphates than Gram-negative bacteria. Long-chain polyphosphates inhibited the growth of Listeria monocytogenes in previous experiments23. However, results of the present study showed that long-chain polyphosphate and medium-chain polyphosphate did not inhibit the growth of Listeria monocytogenes, which might be due to the difference in concentration used.
The addition of polyphosphates to the diet did not promote the growth of broiler carcasses. This is contrary to findings of Moon et al.16 reporting that the experimental group supplemented with long-chain polyphosphate had significantly higher body weight on day 21 as well as daily and weekly weight gain than the control group. Their results suggest that long-chain polyphosphate could promote pre-growth ability of broilers probably because immunity is improved, allowing for improved carcass quality in the pre-growth period. Polyphosphate ions can readily chelate with metal ions. Polyphosphates can make food useful for freshness and antibacterial purposes24,6. Previously, Jensen and Edwards25 have reported significant improvements in body weight, feed utilization, and bone calcification in broilers when 0.1% or 0.2% ammonium polyphosphate is used as a phosphorus supplement in broiler diets for 21 days. The phosphorus content of polyphosphates has an important influence on the growth and development of chickens. Calcium and phosphorus levels of in the diet determine the final level of bone mineralization. Limiting calcium and phosphorus contents can destroy bone strength. In addition, lack of phosphorus in the diet has a significant negative effect on growth in early stages, although this effect disappears in later stages probably because broilers have adapted to this lack of capacity26,27. Sundari et al.28 have also reported the potential of nanocapsule formulations based on turmeric extract and industrial chitosan with sodium tripolyphosphate as a cross-linking agent to improve the digestibility of nutrients. However, research studies using polyphosphates as a poultry feed additive are very limited. Polyphosphates are more widely fed to animals in the form of phosphorus sources. The present study did not achieve the expected effect, which might be related to the concentration of polyphosphate. When testing the whole carcass quality of broilers, only broilers in the experimental group fed with LCPP were affected. They showed a reduction in liver weight. The weight of the liver is directly proportional to body weight29. Moon et al.16 have reported that long-chain polyphosphates do not change liver weights of broiler chickens. LiverS of animals fed a low-calcium polyphosphate diet have 12% lower iron content30. Noteworthy, high (1.0%) or low (0.1%) dietary inorganic phosphate intake can negatively affect brain, lung, and liver development in mice, and another study has reported that adding 10% sodium trimetaphosphate to the diet of mice can result liver weight and slow bone growth and development31,32. This could be one of the causes for the general decrease in liver weight shown in results of the present study. The liver is an important metabolic organ. It helps the body to eliminate harmful substances. Excessive concentrations of polyphosphates have the potential to alter properties of organs in the body as they might show increased toxicities under certain circumstances.
Polkinghorne and Thompson33 have reported that supplementation with selenium or vitamin E can actually prevent meat discolouration by reducing cell damage caused by oxidative processes. In the evaluation of carcass quality of broiler chickens, meat colour, meat brightness values, and so on are taken into account34. Polyphosphates can increase antioxidant activity of the object35. In this study, polyphosphates did not trigger a critical point for the effect of changing flesh color or pH value.
Early studies have shown that chicks fed penicillin antibiotics have improved nutrient absorption and utilisation due to a reduction in intestinal weight36. The reduction in intestinal size in chickens might reflect more efficient nutrient absorption and utilisation, with probiotics improving intestinal nutrition and health. Antimicrobial feed additives can act during early intestinal growth37. Long-chain polyphosphates can help heal ulcerative colitis38. Moon et al.16 have shown that the addition of long-chain polyphosphates can reduce the length and weight of the jejunum, ileum, and cecum. This might be due to polyphosphates' antibacterial capabilities and ability to maintain environmental balance of bacteria in the gut, ths allowing for optimal early intestinal growth.
Activities of polyphosphates depend on chain length. Polyphosphates can impair pathogen clearance, antagonize phagocyte recruitment, reduce phagocytosis, and decrease iNOS and cytokine production. They can also regulate the expression of regulatory genes in macrophages, helping to keep them away from immune exertion of the host39. Monophosphate could not promote the inflammatory response of macrophages. Thus, polymerization of phosphate might be the key to promote inflammatory response. Effects of polyphosphates on lipopolysaccharide-induced macrophage inflammation was more significant when the chain of polyphosphate was longer than 65 monomers. Previous results have shown that polyphosphate-amplified lipopolysaccharide could induce inflammatory responses of macrophages, which provides a new therapeutic target for inflammatory diseases40. High levels of poly-p can reduce the ability of neutrophils and macrophages to phagocytose bacteria and decrease the expression of macrophage attracting chemokines (such as CCL2 and CXCL10) and activating cytokines (such as INFβ) in a Poly-P dose and chain length dependent manner41. Interleukin-1b (IL-1β) and interleukin-1 receptor antagonist (IL-1RN) are cytokines that play a key role in regulating inflammatory responses of gastrointestinal mucosa42. The dephosphorylation function of wheat phytase can greatly promote the secretion of cytokine TNF-α, in which case the immunity of macrophages in the host body can counteract some damage caused by long-chain polyphosphates43. It has been found that the shortest polyphosphate (n = 13) induces milder acute inflammation and produces effective hemostasis when bound to hyaluronic acid44. Polyphosphate-induced platelet-derived mediators can ameliorate intestinal inflammation and colonic epithelial injury by promoting epithelial cell growth through activation of the ERK signaling pathway45,46. In summary, short-chain polyphosphates might be more helpful in promoting the expression of inflammatory cytokines. On the other hand, since the cecum has more bacterial abundance than the jejunum and ileum and long-chain polyphosphates have superior expression of pro-inflammatory cytokines in the environment of the cecum, we speculate that this mechanism might be somehow related to antibacterial activities of polyphosphates themselves.
It has been suggested that higher levels of GLU and TG might be due to enhanced insulin resistance and reduced GLU tolerance caused by metabolic programming for early malnutrition47. TG is associated with the ability of broilers to deposit fat. TG is a class of neutral lipids that play a key role in cell growth, metabolism, and function as a source of energy for the body48,49. Moon et al.16 have reported that long chain polyphosphates do not affect levels of GLU or TG. Because the level of glucose metabolism determines fat content50, broiler's own body condition and ability to consume a diet are also factors worth considering.
Inhibition of bacterial growth by polyphosphates has been demonstrated7. Lactobacillus is a Gram-positive bacterium with beneficial effects on the health of the intestinal tract51. It has been found that 700 pi chain length of polyphosphate accumulated in Lactobacillus paracasei is effective in promoting a healthy human gut52. Coliform bacteria, Shigella, and Salmonella are harmful bacteria that can cause microbial contamination and increase the risk of disease in humans53,54. Thomson et al.55 have reported that the addition of 6% phosphate to hot water (70 or 90 degrees Celsius) has a significant delaying effect on oxidative deterioration of chicken meat throughout 26 days of storage. According to previous results, polyphosphates of different chain lengths all increased the abundance of beneficial bacteria in the intestine, controlled the abundance of harmful bacteria, improved the intestinal environment, and became a good part of the intestinal mechanism.
The posterior phylum is correlated with the phylum Bacillus and the production of short-chain fatty acids such as butyric acid and acetic acid56. Mycobacterium species can enhance the immunity of the body by interacting with the host’s immune system57. Clostridia are an important component of the native bacteria in the large intestine. They are involved in maintaining overall intestinal function58. Polyphosphates are involved in the basal metabolism of bacteria. Microorganisms are very dependent on their environment, especially in extreme environments where the preservation of Pi and energy is critical. Polyphosphates can act as flexible molecules and short-term sources of energy released during its hydrolysis59. MCPP can increase the abundance value of bacteria in the intestine, which is inseparably related to its good antibacterial ability.
In conclusion, it was demonstrated that SCPP, MCPP, and LCPP could improve the internal environment of the intestine. These polyphosphates had significant antimicrobial and anti-inflammatory properties with positive effects on intestinal flora and traits. In the future, the situation for the application of polyphosphates of different chain lengths in poultry and livestock is very clear. Subsequent experimental studies are needed to confirm these findings.