Lysozyme

Lysozyme (Lysozyme) was discovered by Fleming (Fleming; 1922) initially in tears, but later found in other secretions and in the tissues of humans, animals, and some plants. L. is characterized by its ability to rapidly dissolve bacteria, mainly saprophytes. The bacterium found by Fleming in the air, Micrococcus lysodeicticus, is particularly easily dissolved by lysozyme and served as an indicator for the presence of L. for Fleming. This coccus is dissolved by L. in 30 seconds at 37° and even faster at 45-50°. For example, to 5 million cocci contained in 1 cm³ of liquid, 10 cm³ of tears are added; the turbid liquid quickly becomes transparent due to the complete dissolution of the cocci. The fecal streptococcus dissolves more slowly under these conditions - within an hour or more. Dead bacteria are dissolved as well as living ones, which distinguishes L. from bacteriophage. L. diffuses through agar. The experiment is conducted as follows: a circle is cut out from the center of the agar plate, the resulting depression is filled with 10 cm³ of tears or egg white solution and covered with melted agar. Then the entire plate is poured with fresh agar and seeded with Micrococcus lysodeicticus. In the area of L. distribution, the micrococci disappear. The distribution of L. in the human body is peculiar. In synovial fluid, L. is found at a dilution of 1 to 90 (acts on the coccus for an hour at 45°); in glands - 1 to 1,000; in cartilage - 1 to 1,300; in tears - 1 to 40,000; in nasal mucus and sputum - 1 to 13,500; in saliva - 1 to 300. It is also present in leukocytes. Ether does not interfere with its action. L. is particularly abundant in chicken egg white: 1 to 60 million. Cartilage and fish roe also contain a lot of L. Animal tears are 30 times less effective than human ones. - In attempts to isolate lysozyme, Fleming first noted that the active substance was even retained by paper filters, but it then turned out that as filtration continued, L. passed through in increasing quantities and best of all in a 0.5% solution of NaCl. Wolff managed to separate L. from proteins by precipitating the latter with colloidal iron oxide, evaporating the filtrate at low temperature, purifying by dialysis, and precipitating with acetone. By this method, he obtained 3 mg of dry substance from an egg. L. acts only at neutral reaction. In protein fluids, it is destroyed at 75°, but in tears only by boiling. However, Marguerite Bordet (M. Bordet) found that acidified with 0.5% acetic or lactic acid, L. withstands boiling. It can be precipitated from an acidified solution with alcohol and extracted from the precipitate with physiological solution containing 0.2% acid. In the alcohol precipitate, L. retains its strength for a year. However, it is less resistant to various antiseptics than, for example, staphylococcus. L. acts differently on various bacteria. Of 104 species of bacteria from the air, 75% were dissolved by L. from sputum (1:100) and 28% of them were completely dissolved within an hour. L. acts least on the group of intestinal bacteria. In addition, L. from various secretions differs in its action. Thus, tears, so active against Micrococcus lysodeicticus, dissolve other cocci worse than synovial fluid or sputum. It deserves special attention that L. increases in its activity after dissolving bacteria. Thus, after dissolving 30 million cocci in 1 cm³, the lytic power of tears increased 4 times. Under proper conditions, L. acts more energetically than ordinary antiseptics - stronger than iodine 1:100, phenol 1:20, sublimate 1:1000, etc. Bacteria can become resistant to L. and maintain this resistance for nine months when subcultured. At the same time, they acquire resistance to the bactericidal properties of blood and to phagocytosis. It was not possible to increase the production of L. by the body, for example, through vaccination. Fleming sees in this an additional indication that the secretion of L. relates not to acquired, but to natural immunity. On the other hand, Findlay found that when vitamin A is absent from food, L. disappears from tears. This may explain the development of keratomalacia and corneal ulcers in this avitaminosis. This keratomalacia can be prevented by washing the cornea with human tears, but not with physiological solution. The facts presented indicate the importance of L. in protecting mucous membranes from the invasion of microbes. It was previously thought that various secretions played only a mechanical role in this protection by removing microbes. The presence of L. in them indicates their bactericidal action. L. however acts only on saprophytes, not on pathogenic bacteria. Fleming's research on the action of L. on two pairs of extremely similar bacteria is interesting in this regard: 1) Micrococcus melitensis Brucei (=Brucella melitensis) and Bact. abortus Bang (=Brucella abortus) and 2) Bac. pseudotuberculosis rodentium and Bac. pestis. The abortion pathogen is almost indistinguishable from the Malta fever pathogen by ordinary bacteriological methods; if subjected to the action of L., they can be easily distinguished: L. dissolves Bruce I abortus and does not act on Bruce II melitensis. The same relationship was established between the harmless for humans bacterium of rodent pseudotuberculosis and the plague bacterium: only the first is dissolved by L. Thus, L. represents those substances, still little studied, which were first described under the name of bacteriolysins (Gamaleya), then found in bacterial cultures by Much, Rosenthal and others. (see Lysins). But L. was discovered in the human body and has been studied better than its predecessors.