Antibacterial characteristics in the feces of breast-fed and formula-fed infants during the first year of life

Background: Human milk is known to protect infants front a number of infectious diseases. Much less is known about the bioactivity of milk-derived factors in the intestine. In this study, potentially protective characteristics in the feces of breast-fed and formula-fed infants were compared. Methods: The feces of 26 breast-fed and IS formula-fed infants were collected during the first year of life. In each sample, the concentrations of total protein, immunoglobulin A, and sialic acid were measured. In addition, the effect of the fecal samples was measured on the adhesion of enteropathogenic Escherichia coli (EPEC) to Caco-2 cells and on transepithelial electrical resistance (TER) during an infection. Results: In the first month, sialic acid and immunoglobulin A were found in the feces of breast-fed infants in substantially higher concentrations than in the feces of formula fed infants (sialic acid, 1197 +/- 370 mug/ mL versus 31 +/- 19 mug/ mL; immunoglobulin A. 0.11 +/- 7 mg/mL versus 0.3 +/- 1 mg/mL) and thereafter decreased to similar levels in half a year. Adhesion of EPEC to Caco-2 cells was inhibited between 65% and 85% by stools from both groups, The decrease of TER during EPEC infection was unaffected by fecal samples of any origin or age. Conclusion: Potentially protective factors are present in higher concentrations in the stools of breast-fed infants than in stools of formula-fed infants. Interestingly, feces from breast-fed and formula-fed infants inhibited bacterial adhesion to a similar level. but neither was able to preserve epithelial barrier function.