Hydrolysate of Proteins as the Basis for a Bacteriological Culture Medium. ∗

Abstract

The advantage of a medium, free from antigenic proteins and suitable for the growth of organisms, particularly pathogenic bacteria, is obvious.

Long and Seibert 1 introduced a synthetic, non-protein medium suitable for growth of tubercle bacilli. ZoBell and Meyer 2 have described the adaptation of the Brucella group to a protein or peptone-free environment. Miller and Castles 3 have found that a tryptic digest of egg white, from which the coagulable proteins have been removed, is an excellent basis for a medium for gonococcus.

Twenty grams of commercial, dried, powdered egg white were subjected to the action of 50 cc. of boiling, 20% hydrochloric acid for 10 hours, using a reflux condenser for the purpose. It was found that other proteins, e. g., casein and gelatin, could be substituted for the egg white. Excess hydrochloric acid was removed from the hydrolysate by evaporation to a thick paste and the product diluted with water to 500 cc. This solution was treated with 63 cc. of a solution containing 10.35% sodium hydroxide, 0.67% potassium hydroxide; and 0.03% calcium hydroxide. This composition was chosen to insure the presence of the salts of these metals in a quantity to best meet bacterial requirements. The solution was filtered. About one-fifth of its volume of a carefully prepared aluminum hydroxide cream† was added to precipitate some colloidal matter, and the solution again filtered. The volume of this clear, transparent filtrate was then brought to 1,750 cc. with distilled water and 0.10 gm. Na₂HPO₄ and 0.02 gm. NaH₂PO₄ added for buffer effect. One percent dextrose was added and in the case of the solid medium, 2% agar. The final adjustment of the reaction to pH 7.4 was made by addition of the hydroxide mixture.