YEAST AUTOLYSATE AS A CULTURE MEDIUM FOR BACTERIA

The necessity for conserving meat and meat products during the war has rendered a search for cheaper sources of nutritive media for bacteria highly desirable. Douglas and Gordon in England, and more recently Meyer in this country, have proposed the use of peptic and tryptic digests of-animal tissues as a substitute for meat extracts and peptones. These materials cheapen the cost of media but necessitate the use of a digestive enzyme, usually varying in potency, and of considerable amounts of valuable animal protein. It seemed that some non-animal protein might prove equally satisfactory. Yeast naturally suggested itself as a possible substitute. Extracts of yeast have been used in the past to reinforce peptone culture media. Furthermore, yeast readily undergoes autolysis, in the process of which there are formed varying proportions of so-called peptones and aminoacids, while the vitamines remain intact. Thus yeast autolysate may be expected to contain all the nitrogenous elements required for the growth of bacteria. However, the proportions of the individual nitrogenous elements vary with the conditions and duration of the autolysis. The extent of the influence which such variations may have on the growth of bacteria cannot be predicted on theoretical grounds. Hence it became necessary to search empirically for the conditions required to obtain from yeast a satisfactory. medium for bacteria.