Abstract
To estimate the amount (or potency) of the fibrinolytic “enzyme” formed or secreted by Streptococcus hemolyticus, the following titrative method has been adopted by our laboratory. Standard solutions of fibrinogen and thrombin are prepared from freshly drawn human blood by the method of Tillett and Garner. 1 Serial dilutions (1:2) are made of the broth culture to be tested. To 0.5 cc. of each dilution there is added 1 cc. of the standard solution of fibrinogen. Coagulation is then brought about by the addition of 0.1 cc. of standard solution of thrombin, the fibrinous clot usually forming within 30 seconds, after which each tube is placed in a thermostatic waterbath (37°C). Readings are usually made at the end of 15 minutes, 30 minutes, 60 minutes and 2 hours. The highest serial dilution of the broth culture causing complete liquefaction of the clot by the end of 2 hours' incubation is assumed to contain one arbitrary fibrinolytic unit. From this dilution the number of lytic units per cc. of broth culture is readily calculated.
Using this method, the quantitative laws of fibrinolysin-production have been determined for numerous strains of S. hemolyticus. Typical data thus obtained are recorded in Fig. 1.
From this curve it is evident that the rate of fibrinolysin-production and the rate of test-tube proliferation of streptococci are parallel during the logarithmic phase of population-increase, an apparent quantitative linkage between enzyme secretion and cell-division.
This apparent linkage, however, is not operative beyond the logarithmic phase of population-increase. While with certain strains the fibrinolytic titer remains constant or even increases slightly during the subsequent static phase of test-tube growth, a fairly rapid destruction (or inactivation) of the lytic factor takes place in most older cultures.
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