Effect of lyophilization on viability of Mycobacterium leprae multiplied in nude mouse

In an effort to preserve Mycobacterium leprae in vitro, the effect of freezing and drying, i.e., lyophilization, on viability of M. leprae was studied. The viability of the bacilli was quantitatively measured with foot-pad inoculation method using nude mouse. The results obtained demonstrate that the viability of M. leprae was reduced approximately 10(-2) to 10(-3) from that of the starting material, during the process of lyophilization; no viable bacilli were detected in the lyophilized sample containing less than 1.8 X 10(3) bacilli. On the other hand, the bacilli capable of multiplication in nude mouse foot-pads were found in the lyophilized sample with more than 10(5) bacilli. From the results obtained here, it could be suggested that there might be a possibility to preserve M. leprae in vitro by means of lyophilization.