Survival of Mycobacterium lepraemurium in vitro for thirty years by lyophilization

It was demonstrated that the virulence of Mycobacterium lepraemurium could be maintained in vitro for 30 years when the bacilli from the infected subcutaneous mouse tissue were suspended in 10% bovine serum-water, frozen, dried, and stored in a refrigerator. However, it was noted that a complete loss of virulence occurred when the bacilli were suspended in saline. Thus, the selection of the suspending solution is of the utmost importance in maintaining bacterial virulence by lyophilization.