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Nephelometric Assay of Bovine Antistaphylocoagulase Serum¹

^a Department of Microbiology and Public Health, Michigan State University, East Lansing, Michigan 48823

ABSTRACT

A nephelometric assay of staphylococcal coagulase has been utilized to measure coagulase inhibition by bovine anticoagulase serum. Suitably diluted antisera produced maximal inhibition when incubated with purified coagulase at pH 7.3 in phosphate-buffered saline for 15 min at 22 C or 1 hr at 4 C. Neutralization of coagulase activity was measured as the reduction in the clotting rate of a fibrinogen-plasma substrate, and was directly proportional to the concentration of antiserum over a wide range of coagulase activity. A unit of anticoagulase was defined as the amount of inhibitor that neutralized one unit of coagulase. In addition to the heat-stable (56 C, 30 min) antibody contained in the crude -globulin fraction, a heat-labile, nondialyzable coagulase inhibitor was also detected in the sera from 15 of 16 randomly selected dairy cows.

¹ Published with the permission of the Director of the Michigan Agricultural Experiment Station as Journal No. 4093.