The relationship between length of incubation, bacterial growth and tuberculin yield of a strain of Mycobacterium tuberculosis.
The relationship was studied between length of incubation in a liquid synthetic medium, amount of bacterial growth, pH of the culture filtrate and tuberculin yield of a single strain, DT, of Mycobacterium tuberculosis. No sinple relationship was found between the total crop of bacteria and the tuberculoprotein content of the culture filtrate. On the other hand, protein release and the pH of the culture filtrate were closely related. In each of two trials the bacterial crop increased rapidly during the early period of incubation, although maximum growth was not reached until 9 and 13 weeks respectively. The pH of the culture filtrate reached its maximum at a value of more than 9-0 after 5 weeks incubation and then fell until the 10th week; a second rise occurred until the 13th week when the pH dropped again and levelled off slightly on the alkaline side of neutrality. The rate of increase in tuberculin yield was most rapid during the first 7 weeks of incubation. After this, the rate of increase slowed down but the yield was still rising after 18 weeks. It is concluded that for the large-scale production of mammalian tuberculin by the method used in these trials, it is profitable to incubate production cultures for 14 weeks or longer.