Bacterial infections of the gastrointestinal tract through contaminated water or feed, accentuated by stressors, are one of the main challenges in animal production. Animals from infected schools show deficient digestion of fat and liposoluble vitamins, low production rates due to competition for nutrients between the pathogenic microbiota and the host, resulting in economic losses, not only due to decreased production, but also due to increased veterinary and sanitation costs. Therefore, it is important to achieve a good level of intestinal health and have good preventive measures against intestinal infections and mycotoxicosis to achieve good productivity. The use of organic acids, their salts and derivatives such as fatty acid monoglycerides, in animal nutrition has proven to be an excellent alternative in the face of growing demand of natural products in the food market and aquaculture production. It is important to highlight that the amount of organic acids to be used in feed or water supplementation must be adequate to obtain positive results in productive performance. An excess of organic acids can result in a decrease in productive parameters or the appearance of metabolic alterations: decrease in feed consumption and metabolic acidosis.
Water as a source of infections
Water quality is essential for the growth and development of the different species of interest in aquaculture. It is not only important to ensure a correct water supply, but also to ensure adequate physicochemical and microbiological quality, since, in farm systems, the same water source supplies a large number of pools. In the microbiological aspect, although it does not usually offer the ideal conditions for its development and multiplication, water does allow the survival of pathogens and becomes an effective vehicle for their transmission to both animals and humans. Organic acids have been used in aquaculture production for years, both in feed and in water, and have many advantages and disadvantages that we will develop later. It is important to prepare an adequate treatment plan, using a method or a combination of several, that best suits the needs of each farm, to ensure the maximum microbiological quality of the water.
Organic acids
The acids classified as “organic” used in aquaculture production are carboxylic acids, which, depending on the length of their carbon chain, can be classified as short, medium or long chain acids. Short-chain organic acids (SCFA) are called when it has less than 6 carbon atoms, included in this category, among others, acetic, citric, formic, propionic, lactic or sorbic acid. They are called medium chain (AGCM) when they contain between 6 and 12 carbon atoms (such as capric, caprylic or lauric acid) and long chain (LCFA) when they exceed 12 carbon atoms (such as myristic acid). Although they can be used separately, most commercial presentations include a combination of two or more acids, which can be used freely, their salts (usually ammonium or calcium) or esterified with glycerol. This is explained by its physicochemical properties, its mode of action on the animal and microorganisms, and by the different sensitivities that the latter present against different compounds.
Their mechanism of action
The mechanisms of action of these compounds have been widely studied, as well as their effects on different aquaculture species. Its main actions in the body are due to its antimicrobial effect (both bacteriostatic and bactericidal), antifungal effect, its ability to stimulate hepatopancreas secretions, modify intestinal morphology, lower digestive pH, act as an energy source, and improve digestibility and utilization of minerals and other nutrients. Acid molecules exist in undissociated (H-COOH) and dissociated (HCOO-H) forms, these depend on their pKa value or pH value of the medium in which said acid is 50% in its dissociated form and 50% in its undissociated form, these parameters are different for each acid. The undissociated form is capable of penetrating the cell walls of Gram negative bacteria. Once inside the bacterium, it dissociates releasing a proton (H ) that reduces the cytoplasmic pH and affects the integrity of the cellular DNA chains (which can cause cell death). This pH change forces the bacterium to actively eject protons, until the bacterium runs out of energy and is therefore unable to multiply.
On the other hand, the dissociated forms release protons into the medium, which causes the pH to be reduced and therefore creates adverse conditions for the multiplication of bacteria. Acids with lower pKa (such as formic acid) release more protons into the medium and therefore reduce the pH more than acids with higher pKa (such as propionic acid), the latter will remain mostly in their undissociated form and therefore they will be able to exert their antibacterial effect.
The antibacterial effect of acids in the digestive tract has a double benefit: it not only prevents the multiplication and colonization of pathogens that can affect health and productive performance, but also reduces competition for feed nutrients, so the animal will be able to take advantage of them to a greater extent.
As mentioned, microorganisms have different sensitivities to different organic acids. For example, propionic acid has been shown to have a greater fungicidal effect, while acid Formic acid has been shown to have a greater bactericidal and bacteriostatic effect against Vibrios, Pseudomonas, Green Colonies, Clostridium, Salmonella, Campylobacter or Escherichia species than propionic and lactic acids. Likewise, it has been seen that a lower concentration of formic acid is needed to exert a bactericidal effect against Clostridium perfringens, Campylobacter jejuni or Salmonella typhimurium (minimum inhibitory concentration (MIC) of 0.10%), than against Escherichia coli or Clostridium botulinum (MIC of 0.15%).
Conclusions
It can therefore be concluded that the organic acids in the water have an antibacterial power that helps to control its microbiological quality, in addition to generating beneficial properties for animals, both individually and in combination with other acids. Its use, as well as its combination with other disinfection methods, will depend on the characteristics of each farm, history of water quality and objectives that you want to achieve.