GROWTH OF MYCOBACTERIUM-TUBERCULOSIS IN BCG-RESISTANT AND BCG-SUSCEPTIBLE MICE - ESTABLISHMENT OF LATENCY AND REACTIVATION

Growth of mycobacterial species is controlled by a gene, Bcg (candidat e Nramp). Bcg acts at the macrophage level and is thought to control s ome aspect of macrophage priming for activation. Infection of Mycobact erium bovis BCG-susceptible (Bcg(s)) mice with several different mycob acterial species results in the growth of the microorganisms, while th e growth of the same organisms is controlled in BCG-resistant (Bcg(r)) mice. The capacity of Bcg to control the growth of M. tuberculosis ha s not been extensively explored. The purpose of this investigation, th erefore, was to compare the growth of M. tuberculosis in Bcg(r) and Bc g(s) mice. We found that the growth of tubercule bacilli was different in the lungs and spleens of Bcg(r) and Bcg(s) mice when they were ino culated with fewer then 10(3) CFU of the mycobacterium. The difference s in growth were more easily distinguished in the lungs then in the sp leens. The growth of the microorganisms in both strains of mice peaked between 35 and 43 days, and a latent infection was established by 65 days after initial infection. Activation of the hypothalamic-pituitary -adrenal axis resulted in reactivation of the growth of M. tuberculosi s in both Bcg(r) and Bcg(s) mice. Greater numbers of tubercule bacilli were isolated from lungs than from spleens following reactivation. Th e utility of this mouse model in the study of the establishment of lat ency and reactivation of M. tuberculosis is discussed.