Human milk provides both nutritional and immunologic benefits for the infant. Pasteurized human milk (PHM) is available commercially, but pasteurization has been reported to decrease the milk's antimicrobial properties. Lactoferrin (Lf) is a major human milk protein with antimicrobial activity that is dependent on its iron binding capabilities. This protein has been isolated and purified but never added to PHM. The major aim of this study was to evaluate the addition of Lf in PHM and study its in vitro effects against 3 major organisms in the NBICU, E. coli, E. sakazakii, and group B streptococcus. Human milk samples were collected from mothers with infants in NBICU between the 7th and 112th postpartum day. All lactating mothers were healthy and were on no medications except vitamins with iron. All samples were frozen and used within 4 weeks. Pasteurization was by the Holder method of heating the milk to 62.5°C for 30 minutes. Lf was obtained from recombinant human Lf (Ventria Bioscience, Sacramento, CA). Two Lfs were tested: one with no iron and another that was > 50% saturated with iron (Lf/Fe). 1.1 mg/mL of each Lf were added to the PHM. Bacterial growth of the 3 organisms was analyzed by inoculating 1 mL of 107 bacteria into the milk samples and counting the number of colony-forming units after 3.5 hours of incubation at 37°C. Analyses of variance with the Bonferroni post test were used to analyze the data.
Our study shows that human milk has higher antimicrobial activity against these 3 major organisms than pasteurized human milk. Human milk that has been pasteurized loses this antimicrobial activity, but the addition of lactoferrin with no iron can restore pasteurized human milk antimicrobial activity.