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

Factors responsible for the in vitro growth of Mycobacterium leprae in Dhople-Hanks (DH) medium, and also to improve the technique devised earlier, and the source of the M. leprae used as inoculum, were investigated. M. leprae were obtained from armadillos and nude mice, both inoculated earlier with human- or armadillo-derived M. leprae. The growth of M. leprae in DH medium was monitored using two biochemical indicators. Normal growth was obtained when inocula were from livers and spleens of M. leprae-infected armadillos. The M. leprae harvested from the footpads of nude mice failed to multiply in the same medium. Using inocula from livers and spleens of infected armadillos, a gradual decrease in inoculum size resulted in a proportionately slower multiplication of M. leprae. When the DH medium was supplemented with whole M. leprae, or cell-free extracts of M. leprae, from irradiated livers and spleens of infected armadillos, nude mouse-derived M. leprae exhibited growth in the DH medium in accord with that obtained using armadillo-derived M. leprae. Similar results were obtained with cell-free extracts of M. leprae harvested from non-irradiated livers and spleens of infected armadillos, but no growth was obtained when the medium was supplemented with extracts from livers or spleens of normal armadillos. These results indicate the possible existence of a growth factor in armadillo-derived M. leprae.