Human Milk: Its Lysozyme Content and Bacterial Count

Abstract

There is a constant and striking difference in the bacteriologic findings in the stool of the breast-fed and the artificially fed infant. In the stool of the former gram-positive bacilli predominate, while in that of the latter 1 gram-negative, morphologically dissimilar organisms are in excess.To ascertain the significance of this variation and its importance in the problem of infant feeding were the objectives of this investigation. The introductory phase\p=m-\thestudy of lysozyme in human milk and its relation to the bacterial flora of the milk\p=m-\was begun in 1934 and is the subject of this paper.In 1931 Rosenthal and Lieberman 2 reported the influence of lysozyme in the development of the intestinal flora of infants. They found a lytic principle in the stools of nurslings which they tested against cultures of gram-positive sarcinas. It was inactivated by heating at 65 C. for one and a half hours or by boiling for three minutes. Rosenthal and Lieberman identified this substance as lysozyme. It was absent from the stools of artificially fed infants and from the meconium of nurslings for the first two days, but it was constantly present after the fourth day in the stools of breast-fed babies. Lysozyme was present in all samples of colostrum and breast milk but absent from cows' milk and from the modified milk commonly used in feeding infants. It inhibited growth of Bacillus coli at 37 C, and the organism was lvsed at 56 C. Bacillus bifidus was not disintegrated by lysozyme. Rosenthal and Lieberman concluded that lysozyme tends to stabilize the grampositive intestinal flora of nurslings. term "lysozyme" to this substance, which he found in all human tissues and secretions except in normal urine, cerebrospinal fluid and sweat. It was also present in animal tissues, egg white and turnips.Its characteristic quality was the dissolution of live bacteria in culture. It lysed 75 per cent of one hundred and four strains of bacteria obtained from the air, seven of eight pathogenic organisms, twelve of eighteen strains of intestinal streptococci, B. coli and typhoid bacilli.Fleming observed that lysozyme was soluble in water and in physio¬ logic solution of sodium chloride but insoluble in chloroform, ether and toluene. Lysozyme retained its potency at room temperature, remained active when dried in egg white and was precipitated from albuminous fluids by protein précipitants. Its activity was destroyed by a 5 per cent solution of sodium chloride. The lytic effect was most pronounced at a />h of 7. The thermostability of lysozyme differed somewhat, depend¬ ing on the source of the substance, only seven and a half minutes at 75 C. being necessary to destroy its action in saliva, while it took one hour of boiling to destroy its action in tears. Its optimum activation occurred at 60 C. It did not pass through a collodion membrane and was adsorbed by a porcelain filter, cotton wool, filter paper and charcoal.In a later observation, Fleming and Allison 4 stated that with Micrococcus lysodeikticus as an indicator suspensions ...

Relationships Between Lysozyme Concentration of Human Milk, Bacteriologic Content, and Weight Gain of Premature Infants

“…These bacteria can contaminate the milk, but seem not to be suppressed by the lysozyme after contamination. Our results are contrary to earlier observations, which have shown that the bacterial counts of human milk are reduced by lysozyme during re- o H. BRAUN AND H. SANDKUHLER frigeration (16). Nevertheless, the lysozyme continues to be considered a most important bactericidal factor of human milk that is thought to be directed against bacterial contamination of the excretory ducts of the mammary gland.…”