Elucidation of the antistaphylococcal action of lactoferrin and lysozyme

The cationic tear proteins lactoferrin and lysozyme exhibit co-operative antistaphylococcal properties. The purpose of this study was to determine the mechanism of action of this co-operation on Staphylococcus epidermidis. Following blocking of lipoteichoic acid (LTA) binding sites, the effects on binding of lactoferrin and susceptibility to lactoferrin and lysozyme were determined. The effect of lactoferrin on autolysis and LTA release was also examined. Maximal susceptibility occurred on addition of lactoferrin first followed by lysozyme. Blocking the LTA binding sites both reduced lactoferrin binding and decreased susceptibility. Autolytic activity decreased and LTA release increased in the presence of lactoferrin. These results suggest that binding of lactoferrin to LTA is important in its synergy with lysozyme and interferes with the autolysins present on the LTA. It is proposed that, on binding to the anionic LTA of S. epidermidis, the cationic protein lactoferrin decreases the negative charge, allowing greater accessibility of lysozyme to the underlying peptidoglycan.