Preservation of Mycobacterium leprae in vitro for four years by lyophilization.

Although the viability of Mycobacterium leprae suspended in distilled water with or without 10% fetal calf serum was reduced approximately 10(-2) to 10(-4) from that of the starting material during the process of lyophilization, bacilli capable of multiplication in nude mouse foot pads were found in the lyophilized samples stored for 4 years at 4 degrees C. The multiplication rate of the lyophilized bacilli which were suspended in 10% serum-water was much higher than that of the bacilli suspended in water only. On the other hand, no reduction of the viability of M. leprae suspended in 10% skim milk-water was demonstrated during the process of lyophilization as well as storage for 2 years at 4 degrees C. From the results obtained here, it could be suggested that M. leprae might be preserved in vitro by means of lyophilized M. leprae was extremely stable during cryopreservation when the bacilli were suspended in 10% skim milk-water. Therefore, the composition of the solution for suspending the bacilli is definitely critical for the maintenance of M. leprae viability by means of lyophilization.