THE GROWTH OF MAMMALIAN TUBERCLE BACILLI IN TWEEN-ALBUMIN LIQUID MEDIUM .2. OBSERVATIONS ON THE PROPORTION OF VIABLE ORGANISMS, THE CYTOLOGY, THE VIRULENCE, AND THE ANTIGENICITY AT DIFFERENT STAGES OF GROWTH OF BCG

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Abstract
Elongation of cells is the first change observed after inoculation into the culture medium. This occurs between the 8th and 24th hrs. During the exponential phase the bacilli remain elongated and the nuclear count is high. Following the exponential phase there is a gradual diminution in cell length and also in average numbers of nuclei per bacillus. By the end of the 3d week both values are quite low. The yield of bacteria, in terms of optical density or total count, approaches its max. in 8 days. There is little change between the 9th and the 21st day. During the first 2 days after inoculation the N content remains unchanged while the optical density increases exponentially. However, after this there is a close parallel between the optical density and the total N content. During growth, the proportion of clumps containing several bacilli increases for the first 4 days, remains constant during the next 6 days, and then decreases so that cultures aged 14 days or more consist predominantly of single bacilli or clumps of two or 3 bacilli. Cultures of 21 or 28 days are less effective in producing skin nodules in guinea pigs. Young BCG cultures in the exponential growth phase do not have any enhanced virulence. Age does not affect the immunogenicity of the BCG cultures.