Effect of milk on fibronectin and collagen type I binding to Staphylococcus aureus and coagulase-negative staphylococci isolated from bovine mastitis

Tryptic soy broth (TSB)-grown cells of Staphylococcus aureus isolated from acute and chronic bovine mastitis bound mainly ¹²⁵I-fibronectin (¹²⁵I-Fn), whereas strains of nine species of coagulase-negative staphylococci showed a predominant interaction with ¹²⁵I-collagen (¹²⁵I-Cn) type I. A particle agglutination assay (PAA) was used to examine the interaction-negative staphylococci with ¹²⁵I-Fn and ¹²⁵I-Cn immobilized on latex. All 368 coagulase-negative staphylococci demonstrated high ¹²⁵I-Cn and moderate to low ¹²⁵I-Fn interactions in the PAA. Cn-PAA reactivity was high among strains of Staphylococcus xylosus (84.2%), Staphylococcus simulans (77.8%), Staphylococcus epidermidis (76.7%), and Staphylococcus hyicus (74.3%), whereas all six Staphylococcus capitis strains clumped Cn-PAA reagent. Incubating TSB-grown cells in 10% skim milk for 1 h decreased the ¹²⁵I-Fn- and ¹²⁵I-Cn-binding affinity in most of the S. aureus and coagulase-negative staphylococci, while growth in 10% skim milk for 18 h resulted in more than 90% decrease or complete loss of interaction with these proteins. Decreased ¹²⁵I-Fn binding in the presence of milk was correlated with protease production but not with ¹²⁵I-Cn binding.