Lysozyme is an enzyme present in the body fluids such as sweat, tears, saliva and breast milk. It is also found in egg whites, in the caps that bees use to cover their cells and others. It was discovered by chance in 1922 by Alexander Fleming, an English biologist, the discoverer of penicillin. At the time, scientists considered this finding interesting but not significant, however Fleming predicted that more would be said about the enzyme in the future. Lysozyme is made up of 129 amino acids and is referred to as the "body antibiotic" and the "enzyme of the future." Lysozyme or muramidase is a glycosidic hydrolase that catalyzes the hydrolysis of 1-4-beta bonds between N-acetyl-muramic acid and N-acetyl-D-glucosamine. These two compounds are the major building blocks of peptidoglycans, the polymeric compounds that build the walls of bacterial cells. Lysozyme has bactericidal properties i.e. it kills the bacteria. It operates at pH 5 and is thermally stable. Many types of bacteria are subject to lysis by lysozyme. It is active against gram-positive bacteria such as Bacillus, Staphylococcus and Streptococcus. Today, lysozyme is widely used in cosmetics, pharmacy and the food industry as the preservative known as E 1105. It is made from egg white or milk. However, the expenses are high while using this technology and the activity of the enzyme is low, the raw materials are scarce and there are immunological problems in some people. That's why scientists have developed transgenic plants, animals, and microorganisms that can produce human lysozyme. Microbial expression has the advantage of commercial production, as high manufacturing levels are achieved in a relatively short time. Commercially available is also lysozyme produced by fermentation of a genetically modified microorganism Trichoderma reesei, carrying a gene encoding a lysozyme from Acremonium alcalophilium. This microorganism meets the safety criteria. Lysozyme was first used experimentally in pigs in mid-2000, but no positive effect on growth has been identified.
W. Oliver and J. Wells (2013) conducted experiments on pigs weaned at 24 days of age, which lasted 28 days. Animals were divided into three groups of 64 and were fed a mixture without feed additives, a mixture + the antibiotic carbadox and a mixture + lysozyme 100 mg/kg feed. Pigs consuming feed mix with antibiotic and lysozyme had better growth than the control group (0.433 and 0.421 grams average daily gain vs. 0.398 grams) and at the end of the experiment they reached live weight of 20 and 19.8 vs 18.83 kg, respectively. The results were similar in terms of feed utilization - 0.756, 0.750 and 0.695 kg/kg weight gain.
Later, in 2014, the same authors conducted an experiment with 48 pigs at 10 days of age fed for 2 weeks with a milk replacer, milk replacer + antibiotic, and milk replacer + lysozyme derived from the egg whites of hens. The antibiotic and lysozyme groups had a 12% increase in growth compared to the control group. In the lysozyme group, better morphology of the small intestine was observed and Campylobacter was not found in the gastrointestinal tract. The authors conclude that lysozyme is a suitable alternative to antibiotics in young pigs fed with liquid food.
M. Gong (2014) evaluated the safety of muramidase produced by Trichoderma reesei and demonstrated that the commercial product Muramidase 007 showed no adverse effects in subchronic toxicity studies in rats and broiler chickens.
Similar studies were later conducted by W. Schiffka et al. (2019). In the first experiment, 40 weaned pigs were divided into 3 groups receiving three different doses of muramidase: single - 65000, five fold - 325000, and ten fold - 650000 muramidase units per kg of feed. Enzyme activity is expressed in muramidase units and reflects the ability of the enzyme to lyse peptidoglycans. The authors found no decrease in growth, adverse effects on the health status, hematologic and serum parameters. In the second experiment, 288 pigs were divided into two groups - control and experimental, receiving 50000 units of muramidase. This study found a significant increase in the average daily weight gain over the period from 1 to 42 days and a tendency for better feed consumption.
In the US, an experiment was conducted with 600 pigs at 28 days of age comparing the effect of the antibiotics chlortetracycline + tiamulin, and lysozyme 100 mg/kg feed versus a control group without the use of feed additives. Pigs supplemented with antibiotics and lysozyme were found to have higher growth compared to controls (318, 320 and 288 g/day). The author concludes that lysozyme is a good alternative to antibiotics (I. Mavromichalis, 2014).
W. Long et al. (2015) investigated the effect of administration of different doses of lysozyme on growth, intestinal health, and nonspecific immunity in weaned pigs (0, 30, 60, 90, and 120 mg/kg feed). The experiment lasted 28 days. In conclusion, the researchers noted that lysozyme accelerates the growth of weaned pigs, improves gut health and nonspecific immunity, and the addition of 90 mg/kg feed lysozyme is as effective as the antibiotics colistin sulfate + kitasamycin.
L. Zou et al. (2018) aim to study the effect of exogenous lysozyme on growth parameters, serum and biochemical parameters, immune response and gut health in young pigs. A total of 216 pigs (19.81 ± 0.47 kg) were fed diets supplemented with colistin (control group) or lysozyme - 50 or 100 mg/kg feed for 30 days. Pigs fed the higher dose of lysozyme or colistin had a higher average daily weight gain, compared to the lower dosage group. In animals fed with higher doses of lysozyme and colistin, a higher ratio of the intestinal villi height to crypt depth in the small intestine was found. The authors predict that lysozyme can alter nutrient metabolism by altering the gut microbial function of pigs and conclude that pigs whose feed has been supplemented with lysozyme 100 mg/kg feed have similar growth and intestinal microflora as pigs supplemented with colistin.
Dr. A. Zang and his colleagues at Concordia University have developed a project (2017-2018) and are partnering with Elanco to develop lysozyme supplements to displace antibiotic use in animal feed production. They report disturbing facts, namely that in 2012, about 1450 tons of antibiotics were used in feed, water and injectable products in all species of animals in Canada, and more than 63000 tons worldwide, ten times more than human medicine. In this regard, the search for alternatives to antibiotics is becoming more and more relevant. From the review of published studies and the results obtained with the use of the enzyme lysozyme, it is clear that it is effective in weaned and young pigs, during the period that is most critical and stressful for pig breeding.
We are already witnessing a number of such alternatives that ensure good growth, animal production and good health while protecting the environment and consumer health. Among them, the most popular are probiotics, prebiotics, enzymes, organic acids, herbal extracts, essential oils and more. Research continues to look for natural products with antibiotic-like beneficial effects. Vemo 99 specializes in the production of enzymes and herbal extracts with its products from the VemoHerb and VemoZyme series. Which of the above-mentioned antibiotic alternatives will be chosen by consumers of feed additives is a matter of proven effectiveness and economic efficiency.