IngredientsLysozyme (also called muramidase or N-acetylmuramic acid hydrolase; EC 3.2.1.17) is a protein that exerts its enzymatic activity through the hydrolysis of the β-1,4-glycosidic bonds between N-acetylmuramic acid (NAM) and N-acetylglucosamide (NAG) in the polysaccharide backbone of the peptidoglycans of the Gram-positive bacterial cell wall. Egg white lysozyme consists of a single polypeptide chain of 129 amino acids with a calculated mass of 14.4 kDa.
Lysozyme is a ~14 kDa protein present in many mucosal secretions (tears, saliva, and mucus) and tissues of animals and plants, and plays an important role in innate immunity, providing protection against bacteria, viruses, and fungi. Three main different types of lysozymes are known: the c-type (chicken or conventional type), the g-type (goose type), and the i-type (invertebrate type).
In the animal kingdom, three muramidase types have been identified: the c-type (chicken type), the g-type (goose-type), and the i-type (invertebrates). The c-type lysozyme from hen egg white is a model for the study of protein structure and function.
Human lysozyme (hLYZ) and hen egg white lysozyme (HEWL) are classic C-type model proteins, valued for their physiological relevance and accessibility, respectively. Despite both belonging to the C-type, they share only 60% primary structure homology, yet their tertiary structures — featuring four α-helices, three β-sheets, and four disulfide bonds — are highly conserved, with active sites (Glu35 and Asp53) that catalyze the hydrolysis of bacterial peptidoglycan.
Lysozyme is a naturally occurring antimicrobial enzyme, remarkably widespread in nature — from animals and plants to bacteria and bacteriophages. In animals, it is present in secretions, immune cells, and blood. Lysozyme is a protein occurring in animals, plants, bacteria, and viruses. It can be found in granules of neutrophils, macrophages, and in serum, saliva, milk, honey, and hen egg white.
Lysozyme is a ubiquitous enzyme present in all living organisms and viruses with a wide variability in origin, quantity, structural, chemical, and enzymatic properties. The chicken egg white is the richest source of this enzyme, and it is constituted by about 0.3% of lysozyme.
Lysozyme is found in a wide range of body fluids (e.g., tears, saliva, and urine) and tissues (e.g., respiratory and intestinal tract tissues) and is produced by neutrophils and macrophages.
In infant nutrition, the concentration of human milk lysozyme (e.g., 5.01 g/L in mature milk) vastly exceeds that in bovine or goat milk, underpinning its critical role in newborn defense against pathogens, promotion of beneficial Bifidobacterium colonization, and support of intestinal barrier and immune development.
The lysozyme is eluted from an extraction column, precipitated by pH adjustment, and recovered by filtration. The recovered enzyme is further purified, concentrated as lysozyme hydrochloride, and pasteurized. The lysozyme hydrochloride may be spray-dried for use in a granular form or diluted for use in a liquid form.
Commercial pharmaceutical and supplement preparations of lysozyme include a wide range of delivery forms. These include tablets, capsules, compressed lozenges, chewable tablets, coated tablets, effervescent tablets or granules, gastro-resistant tablets, orodispersible films, orodispersible tablets, and powders for solution; as well as mouthwash and powder for oral solution; cutaneous gel, cream, patch, spray, paste, foam, and shampoo; gargle, nasal wash, nose drops, spray, and gel; and eye solution, gel, and ointment.
The Food and Agriculture Organization/World Health Organization and many countries such as Australia, Belgium, Denmark, Finland, France, Germany, Italy, Japan, Spain, and the United Kingdom have acknowledged the nontoxicity of lysozyme and have approved its use in some foods and in pharmacological and therapeutic applications.
Lysozyme, a bacteriolytic protein discovered by Fleming in 1922 and found to be phylogenetically ancient and almost ubiquitous among living organisms, is probably the most studied enzyme in biology and medicine.
Reporting in the 1 May 1922 issue of the Proceedings of the Royal Society B: Biological Sciences under the title "On a remarkable bacteriolytic element found in tissues and secretions," Fleming wrote: "In this communication I wish to draw attention to a substance present in the tissues and secretions of the body, which is capable of rapidly dissolving certain bacteria." As this substance had properties akin to those of ferments, he called it "Lysozyme."
The lysozyme story began one day in late 1921 when Fleming, who had a cold, made the impromptu decision to culture a sample of his mucus. Fleming observed the bactericidal and bacteriostatic activities of nasal secretions from a patient suffering from acute coryza when he treated bacterial culture plates with this material. He named the activity lysozyme because of its capacity to "lyse" bacterial lawns on a dish. Subsequently, he found lysozyme activity in various human physiological fluids and tissues of animals, as well as egg whites.
Fleming identified lysozyme as an enzyme that attacks the cell walls of bacteria. Although underappreciated at first, Fleming's discovery proved monumental in the field of immunology — and primed the scientist to recognize the potential of the penicillium mold that dropped into his lab dish in 1928. Fleming's study of lysozyme, which he considered his best work as a scientist, was a significant contribution to the understanding of how the body fights infection. Unfortunately, lysozyme had no effect on the most-pathogenic bacteria.
It was only towards the end of the 20th century that the true importance of Fleming's discovery in immunology was realised, as lysozyme became the first antimicrobial protein discovered that constitutes part of our innate immunity.
Lysozymes are naturally occurring enzymes present in a variety of biological organisms, such as bacteria, fungi, and animal bodily secretions and tissues. Lysozyme is also the main ingredient of many ethnomedicines.
Lysozyme was developed into pharmaceutical preparations most extensively in Japan and parts of Asia. It was used in cases of chronic sinusitis, difficulty in expectoration associated with respiratory diseases, bronchitis, asthma, and periodontitis, and the usual daily dosage of lysozyme chloride ranged between 60 and 270 mg. Commercial lysozyme hydrochloride tablets (marketed under brand names such as Leftose and related preparations) have been available over the counter in Japan, Taiwan, and other Asian markets, and have been used for decades as oral anti-inflammatory agents for upper respiratory conditions.
Lysozyme has been used clinically in the treatment of periodontitis, administered in chewing gum, and implemented to prevent tooth decay. Lysozyme has also been used to preserve fresh fruits and vegetables, tofu bean curd, seafoods, meats and sausages, potato salad, cooked burdock with soy sauce, and varieties of semihard cheeses such as Edam, Gouda, and some Italian cheeses.
In winemaking, the egg derivative is used for the control of lactic acid bacteria, and it is considered essential to obtain consistent and high quality. The use of lysozyme in food preservation and cheese-making has a long technological history in Europe, where it is designated food additive E1105 under EU regulations.
Another characteristic of lysozyme is its beneficial influence on the digestive processes in mammals, which is manifested by prompt normalisation of the intestinal flora, with consequent saving or improvement of the nitrogen metabolism. Although found in both the animal and plant kingdoms, lysozyme is currently produced on an industrial scale exclusively by extracting from egg white.
Human lysozyme and hen egg white lysozyme both have tertiary structures featuring four α-helices, three β-sheets, and four disulfide bonds, which are highly conserved, with active sites (Glu35 and Asp53) that catalyze the hydrolysis of bacterial peptidoglycan.
Although lysozymes occur in nature in a variety of sources, not all can be good raw materials for their extraction on an industrial scale. Convenient for this purpose are primarily chicken eggs. It is extracted from egg white, where it constitutes approximately 0.3% of the mass and 3.5% of the proteins.
Lysozyme is a cornerstone of innate immunity. The canonical mechanism for bacterial killing by lysozyme occurs through the hydrolysis of cell wall peptidoglycan (PG). Conventional type (c-type) lysozymes are also highly cationic and can kill certain bacteria independently of PG hydrolytic activity.
The natural substrate of lysozyme is the rigid layer of bacterial cell walls, the murein (peptidoglycan), which is a gigantic polymer of (GlcNAc-MurNAc)n polysaccharide strands crosslinked through short peptide bridges at the lactyl groups of the muramic acid residues. Lysozyme lyses bacteria by degrading their protective exoskeleton, the murein sacculus. The high molecular weight murein is thereby hydrolysed to low molecular weight muropeptides.
Peptidoglycan is composed of polysaccharide chains cross-linked by short peptides. The polysaccharide chains contain alternate units of NAM and NAG. The peptides are bound to the lactate moiety of NAM and usually consist of L-alanine, D-isoglutamic acid (D-isoglutamine in many Gram-positive bacteria), L-lysine or meso-diamino pimelic acid (in Gram-positive and Gram-negative bacteria, respectively), and two D-alanine residues.
The antibacterial function of lysozyme involves a dual mechanism: enzymatic hydrolysis of PG, effective against Gram-positive bacteria, and a cationic antimicrobial peptide-like action that can penetrate Gram-negative bacterial membranes.
Muramidase shows bactericidal activity mainly against Gram-positive bacteria. Cytolytic activity against cells of Gram-negative bacteria has not been proved through the enzymatic mechanism alone. However, this lysozyme response is effective against both Gram-positive and Gram-negative bacteria despite the fact that the PG sacculus of the latter organisms is "protected" by an outer membrane; other factors of the innate immune system, such as lactoferrin and defensins, disrupt the outer membrane to facilitate exposure of PG to lysozyme.
Lysozyme kills gram-positive bacteria through hydrolyzing the β-1,4 glycosidic bond between N-acetylglucosamine and N-acetylmuramic acid in the bacterial cell wall. However, besides its enzymatic activity, it exerts antimicrobial effects through its cationic nature which enables it to bind to negatively charged surfaces, thereby expanding its activity well beyond that of gram-positive bacteria.
In addition to its direct antimicrobial role, more recent evidence has shown that lysozyme modulates the host immune response to infection. The lysozyme-mediated digestion of PG leads to the activation of multiple innate immune receptor families that stimulate pro-inflammatory responses. The antimicrobial function of lysozyme is coupled with an important immunomodulatory role because components released from bacteria in a lysozyme-dependent manner can alter innate immune function.
Monomeric lysozyme demonstrates immunomodulatory effects, including stimulation of phagocytes and TLR/NF-κB signalling, as well as anti-inflammatory activity through JNK pathway inhibition and oxidative stress reduction. The lysozyme dimer induces the production of interferon alpha, modulates the synthesis and secretion of cytokines (interleukin 2, interleukin 6, tumor necrosis factor α) by human lymphocytes stimulated with concanavalin A.
Muramyl peptides (fragments of bacterial cell wall peptidoglycan) exert many effects on the immune system and the CNS, and appear to contribute to non-specific resistance to infection, fever, fatigue, and the pathogenesis of bacterial infection. Synthetic muramyl peptide analogues are currently used as adjuvants in vaccine trials in humans.
The immunomodulatory function of lysozyme has only recently been paid close attention to, although it has been reported for a long time that lysozyme is an important part of biological innate immunity. With the discovery of the immunomodulatory ability of lysozyme, lysozyme therapy has attracted extensive attention in the medical community.
Lysozyme exerts its antiviral effects through multiple mechanisms. Direct mechanisms include inhibiting viral entry by binding to viral particles or cellular receptors, and binding viral nucleic acids. Lysozyme can also regulate the activity of immune cells, such as macrophages and neutrophils, which play crucial roles in defending against viral infections.
Both lactoferrin and lysozyme are "immune sensing" as they may stimulate immune responses or resolve inflammation.
Some studies suggest that lysozyme can bind to chitin or β-glucans in fungal cell walls, altering cell membrane permeability or interfering with nutrient uptake. While not fungicidal at physiological concentrations, lysozyme may contribute to synergistic antifungal effects when combined with other agents, such as amphotericin B or echinocandins.
Reflecting the ongoing arms race between host and invading microorganisms, both gram-positive and gram-negative bacteria have evolved mechanisms to thwart killing by lysozyme. Bacterial cells have developed defense mechanisms that allow them to avoid the action of lysozyme. These are based, e.g., on the production of enzyme inhibitors or modification of the PG. The development of resistance to these enzymes is defined as a rare event, at least in vitro, emerging not through de novo mutations, but through the horizontal transfer of resistance determinants. The clinical use of peptidoglycan-degrading enzymes is considered as being at less risk of resistance, due to their nature as recombinant proteins.
Lysozymes and lysozyme-like enzymes can be used as anti-bacterial agents by degrading bacterial cell wall peptidoglycan, which leads to cell death, and can also inhibit fungi, yeasts, and viruses. In addition to its direct antimicrobial activity, lysozyme is also an important component of the innate immune system in most mammals. Increasing evidence has shown the immune-modulatory effects of lysozymes against infection and inflammation.
Evidence strength: The role of lysozyme in innate immunity is well-established and widely accepted across the scientific literature. The molecular mechanisms are thoroughly characterized in biochemical and cell-based studies. Evidence of its involvement in resistance to bacterial infection is compelling but remains indirect. Direct human clinical evidence that supplemental lysozyme measurably improves innate immunity in healthy adults is limited.
In human milk, the role of lysozyme in reducing microbial infections in the gastrointestinal tract of breast-fed infants has been extensively studied. Most gram-positive bacteria and a few gram-negative bacteria are damaged by human milk lysozyme, which helps to increase the levels of beneficial microorganisms in infants and strengthen their disease resistance.
When lysozyme was added to infant formula, formula-fed infants showed reduced incidences of gastroenteritis and allergies and an increase in beneficial microflora in the gastrointestinal tract. After adding 50 mg/L lysozyme to the milk for premature infants who had the disease for 2–3 weeks, the inflammatory focus in feces disappeared rapidly.
The combinational dosing of human lysozyme and milk protein reduced intestinal dysfunction in Malawian children.
Lysozyme supplementation is a key strategy for the "humanization" of infant formula. Currently, in experimental research and development of such "humanized" formulas, hen egg white lysozyme (HEWL) is the primary candidate under consideration due to cost and scalability constraints, despite human lysozyme offering superior biocompatibility and potentially greater efficacy.
Feeding lysozyme to infants increases the immunoglobulin level in faeces (secretory IgA) compared with the faeces of infants fed formula feed only.
Evidence strength: Evidence for the protective role of lysozyme in human breast milk is strong and consistent. Evidence for the benefit of lysozyme supplementation in infant formula rests on smaller clinical trials and historical observational reports. Evidence for benefit in adult gastrointestinal conditions (e.g., IBD) is preliminary, largely preclinical or based on small case series.
Up-regulation of lysozyme in the GI mucosa is a response directed to the special types of bacteria recently detected in inflammatory diseases. The aim of lysozyme up-regulation is to protect individual mucosal segments from chronic inflammation. The molecular mechanisms connected to the crosstalk between the intraluminal bacterial flora and the production of lysozyme released by the GI mucosae have been discussed in recent literature.
Evidence strength: Current evidence on the up-regulation of endogenous lysozyme in gastrointestinal inflammatory conditions is observational and mechanistic. Controlled human trials of supplemental lysozyme for IBD or similar conditions in adults are absent or very limited in the published literature.
Lysozyme was used in Japan and other Asian markets in cases of chronic sinusitis, difficulty in expectoration associated with respiratory diseases, bronchitis, and asthma, and the usual daily dosage of lysozyme chloride ranged between 60 and 270 mg.
The multifaceted approach of lysozyme makes it a potential candidate for combating respiratory viruses, including influenza and COVID-19. The immunomodulatory effects of lysozyme align with the observed characteristics of severe COVID-19, such as excessive inflammation and cytokine storms.
Evidence strength: Evidence for lysozyme in respiratory conditions is largely derived from decades of empirical clinical use in Asia (particularly Japan) for upper respiratory tract conditions, historical small case series, and mechanistic/in vitro studies. Large randomized controlled trials (RCTs) for respiratory indications are not well-represented in the indexed literature.
While some cases of viral infection are mild, others experience uncontrolled inflammatory responses with oxidative stress, dysregulation of iron, and coagulation. Lactoferrin, ovotransferrin, and lysozyme are abundant, safe antimicrobials that have wide antiviral as well as immunomodulatory properties.
It has been reported that lysozyme chloride at the dose of 60–170 mg for 4–24 weeks reduced the incidence of hepatitis after transfusion from 20 to 8%.
Evidence strength: In vitro antiviral activity has been demonstrated against several viruses. The hepatitis transfusion study is a historical small clinical report rather than a modern RCT. Evidence for antiviral benefit of supplemental lysozyme in humans remains preliminary and largely preclinical.
Studies have shown that the antifungal activity of human lysozyme against common bacteria in patients with chronic rhinosinusitis is more than 80%, including Aspergillus fumigatus, Penicillium sp., Acremonium sp., Candida parasilopsis, and C. albicans.
Evidence strength: This is based on in vitro data from clinical isolates. Controlled clinical trials of lysozyme as a therapeutic antifungal agent in humans are absent from the primary literature reviewed.
Lysozyme added to infant feeding formulas makes them more closely resemble human milk. Lysozyme has been used clinically in the treatment of periodontitis, administered in chewing gum, and implemented to prevent tooth decay.
Evidence strength: Use of lysozyme in oral health preparations has a long history, but formal RCT evidence for meaningful clinical benefit in periodontitis or decay prevention is limited in the indexed literature.
An ovalbumin lysozyme normal saline solution was used to treat chronic leg ulcers in patients who had failed to respond to previous treatment.
Evidence strength: Evidence consists of historical case reports and small observational studies. Controlled trials are lacking.
Lysozyme has been reported to resist the proliferation of tumor cells, such as human gastric cancer cells and lung fibroblasts; human lung and prostate cancer cells; endothelial cells (ECV304); and breast cancer cells and peripheral blood lymphocytes. Many experimental studies on tumor cells have confirmed that lysozyme can inhibit the proliferation of tumor cells. Yabe et al. found that it can inhibit lymphoproliferative tumors by regulating interleukin-2 and then regulating the proliferation of lymphocytes.
Evidence strength: All anticancer evidence for lysozyme is preclinical — derived from cell culture and animal models. There are no published human clinical trials evaluating lysozyme as a cancer therapeutic.
Taking into account the well-known antibacterial, antiviral, antifungal, anti-inflammatory, anticancer, and immunomodulatory activity, lysozyme has great potential, mainly in clinical, feed, and food applications, for treating pathogens of a different nature, and numerous examples have been reported in literature. The continuing increase in bacterial resistance to antibiotics prompts the identification of new molecules or new applications of known compounds, such as the case of lysozyme.
Apart from its own lytic activity, lysozyme is able to potentiate the action of numerous antibiotics; microorganisms partially lysed by lysozyme become more sensitive to antibiotics.
Evidence strength: Synergism between lysozyme and conventional antibiotics has been demonstrated in vitro and in animal models. Human clinical evidence for lysozyme as a standalone or combination antibiotic-sparing agent is very limited and not yet supported by adequately powered RCTs.
Lysozyme amyloidosis (ALys) is a rare form of hereditary amyloidosis that typically manifests with renal impairment, gastrointestinal symptoms, and sicca syndrome, whereas cardiac involvement is exceedingly rare and neuropathy has not been reported.
Proteomic analysis of Congo red–positive renal and GI amyloid deposits detected abundant lysozyme C protein. DNA sequencing of the lysozyme gene in affected individuals has detected heterozygous alterations in the lysozyme gene, causing amino acid substitutions. This hereditary condition — caused by mutations in the lysozyme gene that render the protein prone to misfolding and fibril formation — is distinct from exogenous lysozyme supplementation and is not a risk of consuming lysozyme as a supplement or food ingredient.
The problems associated with folding of muramidase and lysozyme participation in the development of amyloidoses also await full explanation.
The following dosages are as reported in the cited scientific literature and historical clinical records; they do not constitute recommendations.
The European Food Safety Authority (EFSA) has re-evaluated lysozyme (E1105) and found no safety concern at the permitted uses and levels in foods.
The safety of lysozyme has already been evaluated by JECFA (1992) and it is authorised as a food additive in the EU; the manufacturing process of the food enzyme does not introduce substances that could raise safety concerns.
Egg allergy is one of the most frequent food allergies. Lysozyme (Gal d 4) is a component of egg white, which contributes to the clinical response in egg allergic individuals. Allergic reactions in food prepared with lysozyme, for example in cheese and wine, have been demonstrated. The EFSA Panel considered that under the intended conditions of use, there is a risk of allergic reactions upon dietary exposure to this food enzyme for egg allergic individuals.
EFSA notes that allergic sensitisation to lysozyme is common among egg allergic individuals. Reports — including one double-blind placebo-controlled food challenge (DBPCFC) — of allergic reactions to lysozyme and lysozyme-containing foods among egg-allergic individuals are available in the literature. Results from a clinical study on lysozyme-containing cheese do not allow conclusions about the safety of lysozyme consumption in clinically egg allergic individuals.
The EFSA Panel considered that, under the intended conditions of use, the residual amounts of lysozyme in treated beers, cheese and cheese products, as well as wine and wine vinegar, may trigger adverse allergenic reactions in susceptible individuals.
There is currently no research showing drug interactions with lysozyme chloride. The synergistic activity of lysozyme with conventional antibiotics, while demonstrated in vitro, has not been adequately characterized in human pharmacokinetic studies. Lysozyme is able to potentiate the action of numerous antibiotics; microorganisms partially lysed by lysozyme become more sensitive to antibiotics — a consideration of potential clinical relevance when co-administering lysozyme-containing products with antibacterial therapy.
There are few clinical achievements of lysozyme in the human body, and the clinical administration of lysozyme depends more on experience. Existing literature provides evidence on the promising use of lysozyme in human diseases. However, it is largely based on case reports or local studies with a small number of subjects, which cannot be generalized to the global population, and is limited by a lack of follow-up data to support the long-term benefits. The mechanisms of lysozyme's anticancer action and disease marker roles are not clear, and the theoretical basis is incomplete; there are few clinical trials of lysozyme as a drug currently.
Health conditions that Lysozyme may help support.
Body systems that Lysozyme may help support.
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