Growth-determining substances in bacteriological culture media

Abstract

Some months ago a report was made of a series of experiments based on the observation that, while a peptone-free meat infusion broth would produce abundant growth of hemolytic streptococci, short boiling with charcoal removed this property entirely. The addition of commercial peptone or of a sulphuric acid hydrolysate of certain proteins, such as casein or meat, reactivated the charcoal-treated infusion and heavy cultures of streptococci could be obtained on the mixture, while neither one alone gave the slightest trace of growth. It was shown that the activating material in the protein hydrolysate was precipitated by mercuric sulphate, and that it had not been possible to identify it with any of the amino acids known to be precipitated by this reagent either alone or in combination. It is the purpose of the present communication to describe the further purification of this activating material.

Much of the work has been done using a commercial preparation called “aminoids” in place of an acid hydrolysate of casein. This consists of an enzyme digest of milk proteins continued until the product is biuret free. It has been used simply as an economy of time since in handling large quantities the acid hydrolysis is somewhat cumbersome. Every step in the separation, however, has been checked on an acid hydrolysate and it is believed that there is no essential difference in the factors involved.

In attempting to separate the active material from the mercuric sulphate precipitate, fractional precipitation with the same reagent was tried. This led to the discovery that there were two factors in the precipitate, both of which were necessary to reactivate the charcoal-treated infusion. One of these must be carried down by adsorption in the original mercuric sulphate precipitate, or else its solubility is influenced by the presence of other substances, for it is not reprecipitated, to any extent, from the mixture by the addition of mercuric sulphate.