Relationships between lysozyme concentration of human milk, bacteriologic content, and weight gain of premature infants.

Lysozyme concentrations and bacterial colony counts were determined in 399 human milk samples obtained from 42 mothers (18 mothers of term infants, 24 mothers of preterm or small-for-date neonates). The average lysozyme concentration was 21.39 +/- 13.19 mg/L. Lysozyme concentrations were significantly greater in preterm (24.99 +/- 15.05 mg/L) than in term milk (14.89 +/- 9.83 mg/L) (p less than 0.05). Bacterial colony counts did not decline with increasing lysozyme concentration, i.e., no correlation between lysozyme concentration and bacterial count was found. Despite this lack of correlation, a significant correlation between lysozyme concentration and rate of weight gain was observed: the higher the lysozyme concentration, the better the weight gain. The mechanism of this observation remains to be elucidated; a trophic effect of lysozyme is suggested as a possible mechanism.