Effect of Bacteriophage on Strepto-Fibrinolysin Production. ∗

Abstract

To test the effects of bacteriophage on the production of fibrinolysin by hemolytic streptococci, 100 cc. flasks of 0.5% glucose veal-infusion broth (pH 7.4) were inoculated with 0.1 cc. of a 24-hour broth culture of Streptococcus hemolyticus and an amount of bacteriophage ('phage-lysed homologous streptococcus filtrate) demonstrably sufficient to produce lysis was added to each flask. The flasks were incubated at 37°C. with constant stirring and samples were withdrawn at regular intervals for total population counts and fibrinolysin titrations. Composite data from 6 such counts and titrations with 2 different streptococcus-bacteriophage combinations are recorded in Fig. 1.

From this figure it is seen that the initial increases in fibrinolytic titer are roughly parallel with the logarithmic increase in bacterial population. Bacterial lysis is accompanied by a partial (and in some cases nearly complete) destruction (or binding) of the fibrinolytic enzyme. The beginning of a terminal overgrowth with phage-resistant variants, however, is accompanied by a renewed and greatly accentuated formation of fibrinolysin. The fibrinolytic titer at the 24-hour stage of the terminal overgrowth is at least 10 times that of the maximum initial titer with the parent phage-susceptible strain.

In order to confirm these results, phage-resistant variants were isolated in pure culture from such over-growths, and 0.1 cc. of a 24-hour sub-culture of each phage-resistant variant was inoculated into 100 cc. flasks of veal-infusion broth, control flasks being inoculated with an equal volume of a 24-hour broth culture of the homologous, phage-susceptible parent strain.