Optimal pH for preserving the activity of Mycobacterium leprae during incubation of cells in a cell-free liquid medium.

The effect of the pH of a cell-free liquid medium on the activity of Mycobacterium leprae during incubation of the cells was investigated. As a parameter for evaluating the activity, the amount of adenosine triphosphate (ATP) extracted from the incubated cells collected by centrifugation was measured. The results demonstrate that the activity of M. leprae cells was maintained at a significant level for approximately 4 weeks at 30 degrees C in 0.05 M phosphate buffer containing 10% fetal calf serum at pH 7.0 compared to cells at other pHs tested, but activity was not preserved in phosphate buffer at pH 7.0 without serum and incubated at 37 degrees C. The maintenance of the activity under these conditions was prolonged somewhat by the addition of glycerin (2%) to the medium, and was definitely inhibited by rifampin but not by either penicillin or isoniazid. From the results reported here, it could be postulated that the optimal pH of cell-free media for the study of cultivation of M. leprae is 7.0.