ATP content of Mycobacterium tuberculosis grown in vivo and in vitro

In order to determine the reason for the slow growth of Mycobacterium leprae either in a host or in vitro, the growth characteristics of Mycobacterium tuberculosis were studied. The ATP content of in vitro-grown M. tuberculosis was about 520 pg/10(6) viable organisms. The ATP levels from in vivo-derived organisms obtained from liver and spleen of mice was about 130 pg (in cases of chronic infection) and about 270 pg (in cases of acute infection). When the in vivo-derived organisms were inoculated into culture medium, the growth rates for both types of organisms, acute as well as chronic infection, were the same and the maximum growth was reached during the fifth subculture. Although the maximum ATP content for both types of organism was the same, it was attained during the 4th subculture for organisms obtained during acute infection and during the 6th subculture for those obtained during chronic infection. The comparison between the ATP content of M. leprae and of M. tuberculosis indicates the reason for the slow growth of M. leprae.