Identification by mass spectroscopy of F4ac-fimbrial-binding proteins in porcine milk and characterization of lactadherin as an inhibitor of F4ac-positive Escherichia coli attachment to intestinal villi in vitro

Enterotoxigenic Escherichia coli (ETEC) must attach to the intestinal surface to cause diarrhea. Milk and colostrum play an important role in protecting suckling piglets against ETEC through their constituent antibodies as well as non-immunoglobulin factors. We used affinity chromatography and liquid chromatography–mass spectrometry to identify lactadherin, β-casein, whey acidic protein, lipoprotein lipase, and several structural cellular proteins as non-immunoglobulin F4ac fimbriae-binding porcine milk proteins. To determine their potential biological relevance in a digestive environment, we treated porcine milk with pepsin or pepsin–pancreating in vitro, and found that pepsin digestion did not interfere with the F4-binding capacity of lactadherin as well as it revealed a cryptic F4-binding site(s) in α-S1 casein and heart fatty acid binding protein. We also demonstrated that lactadherin interfered with attachment of F4ac-positive ETEC to porcine small intestinal villi in vitro and that this interference was carbohydrate dependent. Thus, our evidence suggests that lactadherin and the other F4-binding milk proteins, together with other defense components of milk, could play a role in protection of neonatal piglets against ETEC induced diarrhea.