Isolation of cultivable mycobacteria from feces and lungs of armadillos infected with Mycobacterium leprae.

In the past, no cultivable mycobacteria were isolated from armadillos captured in the state of Florida, U.S.A. But recent findings of acid-fast bacilli (AFB) in the lungs of armadillos infected with Mycobacterium leprae prompted us to undertake this study to determine the correlation between systemic leprosy infection and the occurrence of cultivable mycobacteria in the lungs and stools of these animals. No AFB could be isolated from noninfected animals. Seventy percent of the infected animals developed disseminated infection, but no cultivable mycobacteria were isolated from their livers and spleens. However, cultivable mycobacteria were isolated from the lungs and stools of a large number of armadillos showing disseminated infection. The most common among these were M. gordonae, M. fortuitum, and M. avium. There was a close correlation between the development of disseminated leprosy infection and the occurrence of cultivable mycobacteria in their lungs and stools, perhaps due to the decline in the immune system in these animals in the later stages of infection.

In vitro and in vivo interactions of drugs used in multidrug therapy in leprosy.

Interactions of different drugs commonly used in multiple drug therapy were evaluated using both in vitro culture (cell-free as well as macrophage) system and mouse footpad. No additive effects were obtained in the in vitro system when dapsone was combined with either rifampicin or clofazimine, while a strong antagonism was observed when clofazimine was combined with rifampicin but not with rifabutin. In the mouse footpad system, a strong synergism was obtained when clofazimine was combined with either rifampicin or rifabutin, but significant antagonism was observed with the combination of clofazimine and dapsone.

Factors influencing the in vitro growth of Mycobacterium leprae: effect of sulfhydryl compounds.

In an attempt to determine the factors that influence the in vitro growth of Mycobacterium leprae in DH medium, the effects of sulfhydryl compounds were studied. Growth of M. leprae was monitored using two biochemical indicators. Only the sulfhydryl compounds, in reduced form, containing carboxyl group could support the growth of M. leprae. Higher cell yields were obtained when these sulfhydryl compounds were supplemented with dithiothreitol, presumable to keep the monothiols in reduced state during long incubation periods. Ascorbic acid could not replace dithiothreitol for this purpose. It is suggested that these carboxylated sulfhydryl compounds play a role in the metabolic activity of M. leprae along with maintaining low redox potential of the medium.

Factors influencing the in vitro growth of Mycobacterium leprae: effect of oxygen.

In our efforts to evaluate factors responsible for in vitro growth of Mycobacterium leprae in DH medium and also to improve the system, effects of oxygen tension on in vitro growth of M. leprae were determined. This was achieved by varying the ratio between DH medium and free air space above the medium in the culture tubes. Growth-competent M. phlei (ATCC 11758) could tolerate all the oxygen it can get in the medium. On the other hand, M. leprae seemed to be of microaerophilic nature. In vivo-grown M. leprae cells were more sensitive than their counterparts that were adapted to in vitro environment. In vivo-grown cells grew better when 70% of the space in culture tube was occupied by DH medium. These in vitro-adapted cells gave optimum growth in subcultures when the air spaces in the culture tubes were 40-50%. The role of oxygen tensions in the development of lesions in leprosy patients and armadillos has been discussed.