Limited in vitro multiplication of Mycobacterium leprae

The inability to cultivate Mycobacterium leprae in vitro has been a major bottleneck in leprosy research. There have been numerous reports on successful in vitro cultivation of this organism, but these reports could not be confirmed by others in the field. Hence, in vitro multiplication of M. leprae was evaluated in various culture media. Only 2 media supported limited multiplication of M. leprae. One medium was used previously by one of the authors (AMD) for in vitro growth of M. lepraemurium and the other was a conditioned medium used for growth of mouse dorsal root ganglion. Growth was evaluated by 3 biochemical parameters: bacterial ATP, DNA and 3H-thymidine uptake. All 3 measurements revealed a 4-6-fold increase in cell biomass after 16 weeks of incubation at 34 degrees C. The harvested bacilli demonstrated a few of the important properties of M. leprae, including growth in mouse footpads. However, subcultures of these in-vitro-grown cells in the respective media could not be achieved. By the end of 12 weeks, the bacilli lost all intracellular ATP and the ability to incorporate 3H-thymidine; they also failed to multiply in mouse footpads.