The protective effect of breast feeding in relation to sudden infant deathsyndrome (SIDS). I. The effect of human milk and infant formula preparations on binding of toxigenic Staphylococcus aureus to epithelial cells

Epidemiological studies indicate that breast-fed infants are at a decreased risk of sudden infant death syndrome (SIDS) compared to formula-fed infant s. Increasing evidence suggests that infectious agents might be involved in some of these deaths, in particular bacteria which colonise mucosal surfac es and produce superantigenic toxins. One species implicated in recent stud ies of SIDS infants is Staphylococcus aureus. We tested the hypothesis that in comparison to infant formula, human milk might be a better inhibitor of binding of S. aureus to epithelial cells. In this study, two protocols wer e used for the binding assays which were assessed by flow cytometry: the in vitro method in which bacteria were treated with milk or formula, washed a nd added to epithelial cells; and a method more closely reflecting the comp etitive interactions in vivo in which cells, bacteria, and milk or infant f ormula were added at the same time. With the in vivo method, breast milk ca used enhancement of bacterial binding to cells whilst infant formula caused inhibition; however, for the in vitro method, both human milk and infant f ormula caused consistent enhancement of binding. Flow cytometry and light m icroscopy studies indicated that the enhancement was due to the formation o f bacterial aggregates. Human milk and infant formula preparations were als o compared for components (antibodies or oligosaccharides) that could inhib it binding of S. aureus using the in vitro method. Human milk contained bot h IgA and IgG. Neither human milk nor infant formula contained oligosacchar ides reactive with the Ulex europaeus lectin but both contained components that bound monoclonal antibodies to Lewis(a) and Lewis(b) antigens which ca n act as receptors for S. aureus. With both methods, synthetic Lewis(a) and Lewis(b) inhibited S. aureus binding in a dose-dependent manner. With huma n milk, however, the only component which showed a significant correlation with inhibition of binding was the IgA specific for the staphylococcal surf ace component that binds Lewis(a), Both human milk and infant formula conta in components which could potentially inhibit bacterial binding but only br east milk contains the IgA specific for the bacterial adhesin that binds Le wis(a). Studies using the in vivo method suggest that protection associated with breast feeding in relation to SIDS could be due mainly to the formati on of bacterial aggregates. The studies have implications far Further resea rch into constituents of infant formula. (C) 1999 Federation of European Mi crobiological Societies. Published by Elsevier Science B.V. All rights rese rved.