Effects of powdered human milk fortifiers on the antibacterial actions of human milk.

OBJECTIVES: To evaluate the effects of powdered fortifiers and the addition of iron and medium-chain triglycerides on preterm human milk antibacterial activity.

STUDY DESIGN: Human milk samples were obtained from 42 preterm lactating mothers after the first week of postnatal life. Enfamil (EHMF) and Similac (SHMF) Human Milk Fortifiers were evaluated. All mothers were healthy and were on no medications except for vitamins during lactation. The effects of each fortifier against E. coli (E. coli), Staphylococcus (Staph), Enterobacter sakazakii (ES), and Group B Streptococcus (GBS) were measured by the filter paper method and growth of the bacteria with human milk alone as control. The addition of iron and medium-chain triglycerides (MCT) to human milk was also tested.

RESULTS: Human milk inhibited the growth of E. coli, Staph, ES, and GBS. Only the SHMF and the addition of MCT had similar antibacterial action as human milk alone. EHMF and the addition of iron to human milk removed the milk's antibacterial action against these four organisms.

CONCLUSIONS: Preterm human milk has antimicrobial activity against E. coli, Staph, ES, and GBS. This activity can be affected by the addition of iron and fortifiers that contain iron.