Staphylocoagulase has been tacitly assumed to play an important role in the virulence of Staphylococci and also it has been considered by most that M-protein might have a significant role in the Streptococcal infection. However, few direct demonstration of its role in the pathogenesis of infection with virulent, coagulase positive, and avirulent, coagulase negative staphylococci has been made.
The results presented here show that when virulent, coagulase positive and avirulent, coagulase negative Staphylococci are suspended in solutions of purified coagulase prepared by Blobel's method or in solutions of purified M-protein of Group A Streptococci (Type 6, 5-43-M) prepared by Slade & Kimura's method and injected intracerebrally into mice, the slight or marked increase in the virulence of the organisms results. As the test strains of Staphylococcus, Staphy. aureus (A-II), coagulase positive virulent strain, and Staphy. epidermidis (B-2, B-7, B-12), coagulase negative avirulent strain were used. These strains tested were all isolated in the authors laboratory. The results show that virulent Staphylococcus was slightly increased by the addition of coagulase or M-protein and one out of three avirulent Staphylococci remarkably increased the virulence by the addition of coagulase and one out of two avirulent strain remarkably increased the virulence by the addition of M-protein.