ABSTRACT A total of 103 Staphylococcus a w e w strains isolated from bovine mastitis were tested for bovine lactoferrin binding in a 1251-labeled protein binding assay. More than 85% of the strains demonstrated high to moderate and a few showed little or no binding. Bovine lactoferrin binding to S. aureus cells was high when grown on blood, nutrient, or proteose-peptone agar, but the binding capacity was low with cells grown on salt rich media, in skim milk, or in broth. The kinetics of 1251-labeled bovine lactoferrin binding required approximately 90 min for complete saturation with optimal interaction in the pH range 4.0 to 7.0. The lactoferrin-staphylococci interaction was specific with a high affinity (association constant, K, 14 x 106 L/mol). Scatchard plot analysis estimated the number of binding sites per cell at 7200 on strain SA-340. Unlabeled bovine lactoferrin effectively displaced the binding of the labeled ligand to strain SA-340 in a dosedependent manner. Abbreviation key: bLf = bovine lactoferrin, hLf = human lactoferrin, HRPO = horseradish peroxidase, Lf = lactoferrin, PBS = phosphatebuffered saline, PMN = polymorphonuclear leukocytes
