Protection of Suckling Mice from the Heat-Stable Enterotoxin of Escherichia coli by Human Milk

Human milk contained a factor or factors that protected suckling mice from lethal fluid loss due to Escherichia coli heat-stable toxin. This protective effect was present throughout lactation. The factor was heat stable, acid and alkali stable (pH 2 and 12), and of low molecular weight. Ion-exchange chromatography indicated that it was uncharged at neutral pH. The factor was insensitive to proteinase K digestion and partitioned in the aqueous phase in 2:1 (vol/vol) chloroform-methanol. Acid hydrolysis (2 N HCl at 100 C for 3 hr) destroyed the protective effect. Neither an amino acid mix simulating human milk nor lactose in phosphate-buffered saline was protective. These data indicate that the protective factor in human milk is neither a lipid nor a protein but appears to be a carbohydrate.