Latex agglutination test to identify coagulase, clumping factor and protein A produced by staphylococci

Since a rapid latex agglutination method for identifying Staphylococcus aureus has recently been described, we attempted to identify which factors in staphylococci produce a positive reaction so as to indicate the possible applications and limitations of the test. Latex particles prepared with human plasma (latex-plasma), immune serum globulin (ISG) (latex-ISG) or bovine fibrinogen (latex-fibrinogen) were evaluated. Purified protein A or staphylococcal colonies possessing protein A caused latex-ISG and latex-plasma to agglutinate. Colonies which had clumping factor (CF) caused latex-fibrinogen and latex-plasma to agglutinate. A factor, with molecular weight and physical properties identical to staphylococcal coagulase, present in the supernatant of overnight broth inoculated with S. aureus caused latex-fibrinogen and latex-plasma to agglutinate but not latex-ISG. Thus, when latex particles are prepared using plasma, the preparation appears to identify coagulase, CF and protein A.