The rate of growth of virulent and avirulent streptococci in serum media.

Abstract

In a series of experiments which we reported in 19211 we found that after strains of beta type streptococci had been rendered virulent for mice by animal passage cultures of the virulent streptococci grew more slowly during the first few hours after they were inoculated into broth to which horse serum had been added than did cultures of the avirulent forms of the same strains. In comparing the growth of the virulent and the stock cultures of these streptococci bacterial counts were made at hourly intervals and the amount of hemolysin produced in the cultures was titrated with standardized suspensions of erythrocytes obtained from defibrinated horse blood. The amount of hemolysin produced at these intervals in these cultures corresponded with the rate of growth of the bacteria. The virulent streptococci grew slowly after they were inoculated into the broth, then after a latent growth period of several hours grew very rapidly until the sixteenth hour, after which the bacterial count gradually fell. The maxi...