A method for the measurement of fibrinolysin production by beta hemolytic streptococci is described. The test was shown to be highly accurate in that repeated determinations showed only small variations. A study of 766 strains of beta hemolytic streptococci isolated from normal soldiers and patients with respiratory disease showed that fibrinolysin was produced by Lancefield groups A, C, and G, and, in addition, by a few strains of groups B and F.
Group A streptococci produced more fibrinolysin on the average than the other groups. The median titers were 117 for group A, 61 for group C, and 20 for group G streptococci. In a study of 388 typed group A streptococci from different subjects the fibrinolytic capacity of an organism was shown to be related to the serological type. The importance of this observation in relation to the role of streptococcal fibrinolysis in infections is discussed.
Finally, it was demonstrated that strains of streptococci which produced large amounts of fibrinolysin were capable of stimulating antifibrinolysin formation in patients whereas strains that produced small amounts only occasionally caused antibody formation.