The uptake of 3H-thymidine in Mycobacterium leprae inoculated mouse macrophage cultures as a rapid indicator of bacillary viability. Factors influencing the specificity of the in vitro assay.

Mouse peritoneal macrophages derived from BALB/c were used as host cells for 17 human-derived M. leprae strains. Simultaneous pulsing with 3H-thymidine (3H-Tdr) showed uptake of the radiolabel in 58.8% of the bacilli over a 14 day period. Preliminary data of three M. leprae strains indicate that the 3H-Tdr is preferentially incorporated into the mycobacterial DNA and not into the mammalian host cell DNA. This in vitro assay provides a rapid assessment of M. leprae viability. The factors influencing the uptake of 3H-thymidine are described.