Demonstration of staphylococcal clumping factor and free coagulase in soft agar media.

Of the methods now available for the detection of coagulase positive staphylococei, none is designed to show both clumping factor and free coagulase activity in a single system. The observations reported here are by-products of a search for variant strains of staphylococci with particular reference to strain differences in the cell surface component known as clumping factor or bound coagulase. In this search, the soft agar technique, which has been applied to variation studies by a number of workers (McCarty et al., 1946; Pike, 1946; Pittman and Davis, 1950; Lankford et al., 1955; Finkelstein and Sulkin, 1958), has proved most rewarding. A conmparison of the reactions of staphylococei in various soft agar media with the results of conventional coagulase and agglutination tests led to the method described here for simultaneous detection of free coagulase and clumping factor. The study also revealed that the formation of compact staphylococcal colonies in serumand plasmasoft agar need not be due exclusively to antibody action.