Particle agglutination assays for rapid detection of fibronectin, fibrinogen, and collagen receptors on Staphylococcus aureus

Abstract

Latex beads (0.8-μm diameter; Difco Laboratories) were coated with fibronectin, fibrinogen, collagen type I, or denatured collagen (gelatin) and evaluated in a particle agglutination assay (PAA) for the rapid detection of fibronectin, fibrinogen or collagen binding to Staphylococcus aureus. These assays were compared with a commercial test for detecting the binding of fibrinogen and immunoglobulin G (Staphaurex). Bacterial cells (approximately 1010 cells per ml) suspended in 0.02 M potassium phosphate buffer (pH 6.8) caused the clumping of standard fibronectin, collagen, gelatin, and fibrinogen latex suspensions within 2 min on glass slides. The test results were scored semiquantitatively from strongly positive (+++) to weakly positive (+) and negative (-) reactions. The negative PAA reactions corresponded to a median value of 11.5% relative to the binding of 125I-labeled protein to strain Cowan I, indicating the high sensitivity of the test. The reaction with fibronectin and fibrinogen latex suspensions and with Staphaurex were optimal for cells grown on tryptic soy and brain heart infusion both media. Blood agar was optimal for reactions with collagen and gelatin latex suspensions. Media containing high salts (mannitol salt agar and staphylococcus medium 110) enhanced the tendency of cells to autoaggregate. These assays were also clinically evaluated on 187 S. aureus isolates. The PAA reagents were stable, and the assays were highly specific, sensitive, and reproducible, thus making PAA suitable for the rapid screening of the binding of various bacterial pathogens to serum and connective-tissue proteins.