Experiments were performed to determine the mechanism by which Erysipelothrix rhusiopathiae clots plasma. Detection of plasma-clotting activity in four strains of E. rhusiopathiae was carried out by mixing a 24-h broth culture of a tested bacterial strain with rabbit plasma (tube coagulation test). Sodium citrate, sodium oxalate, EDTA, and heparin were used as anticoagulants in preparing the rabbit plasma. E. rhusiopathiae strains clotted solely citrated plasma in 18 to 24 h. A known coagulase-positive strain of Staphylococcus aureus clotted all of the plasma preparations within 1 h. Various constituents of the organisms, such as cell-free culture filtrates, sonicated extracts, and Formalin-killed bacteria, were also checked for their ability to clot citrated plasma. No constituents of any strain of E. rhusiopathiae clotted the plasma. Only culture filtrates of S. aureus clotted the plasma under these conditions. The spectrophotometric assay demonstrated that two plasma-clotting strains of E. rhusiopathiae consumed the citrate in the plasma just before clotting. Of 301 veterinary clinical isolates of E. rhusiopathiae, 267 (88.7%) were positive in the tube coagulation test. On the basis of these results, it was concluded that plasma clotting by E. rhusiopathiae was due not to extracellular factors such as staphylocoagulase but to consumption of the citrate in the plasma.
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