The antiinvasive effect of bovine lactoferrin requires an interaction with surface proteins of Listeria monocytogenes

The anti-invasive effect of bovine lactoferrin (BLf) and of bovine transferrin (BTf) towards L. monocytogenes, an intracellular facultative food-borne pathogen, was assayed in the enterocyte-like cell line Caco-2. When 0.5 mg/ml BLf were added during the infection time or preincubated with bacteria the number of internalized bacteria was noticeably decreased whereas BLf was ineffective when preincubated with the enterocytes or added post infection. BTf was deprived of any effect. Results from direct binding and Western blotting assays provided evidence that two L. monocytogenes surface proteins, of approximately 80 and 60 kDa, specifically reacted with BLf. These findings strongly support the hypothesis that the antiinvasive mechanism of BLf is due to its interaction with bacterial surfaces, but not to its binding with eukaryotic cells.