Dissociation of a Streptococcus Hemolyticus.

A hemolytic streptococcus was isolated from 1 of 50 guinea pigs dying during an epidemic of streptococcus infection. The organism under consideration is also pathogenic for white mice, white rats and rabbits. The plates made from the heart's blood of the original guinea pigs showed for the most part colonies of a typical virulent streptococcus, except for 2 colonies which were flat, translucent, yellowish and conspicuously large. After fishing and replating these 2 colonies, the above characteristics were accentuated except for the fact that they were less flat. In broth the growth was homogeneous in contradistinction to the flocculent growth of the ordinary virulent type of hemolytic streptococcus.

The organisms from the particular colony under discussion have certain unusual characteristics. Apparently they remain true to type, no matter how they are cultivated or passed through animals. They also maintain their virulence after standing at room temperature in plain broth for 2 or 3 months and on repeated subcultivation. The virulence is such that 1/4 cc. of a 16 hour growth diluted 1-100,000,000 will kill mice.

The organisms of the conventional colony mentioned above behave, as far as virulence is concerned, as any hemolytic streptococcus. However, upon clutivation in broth of a pH 6.5 and upon rapid mouse passage a few of the flat, Translucent colonies eventually appear. On mouse passage they are recovered first from the peritoneal exudate rather than the heart's blood and apparently always predominate in the former. The organisms forming the flat colonies were found to be encapsulated when taken directly from the mouse, in contrast to non-encapsulated forms of the ordinary virulent streptococcus under similar circumstances.