Preservation of Mycobacteria: 100% Viability of Suspensions Stored at -70 C

Abstract

Our earlier studies on long-term preservation of mycobacteria have been expanded to include other species in this genus. Mycobacterium kansasii and M. marinum , like mammalian tubercle bacilli and BCG, survive much better when stored at -70 C. By statistical analysis, M. gordonae, M. scrofulaceum, M. xenopi, M. avium, M. intracellulare, M. terrae, M. fortuitum , and M. smegmatis survived equally well at -20 C or -70 C; however, viable counts of all strains stored at -20 C were always lower than those of paired suspensions stored at -70 C, suggesting that the lower temperature is preferable for prolonged storage periods. Advantages of preservation at -70 C in Tween-albumin liquid medium are: (i) 100% viability of bacterial populations for long periods, (ii) highly reproducible inocula for animal experiments, (iii) minimal clonal selection of undesirable mutants, (iv) maintenance of genetic characteristics, and (v) adaptability to a “seed lot” system. On the basis of available information, a discussion of lyophilization versus freezer storage is presented.