The Effect of Long-Term Storage on Mycobacterium bovis.

It was established that when stored for many years (10-13 years) in low-temperature conditions (3°C), without sub-culture on a nutrient medium, Mycobacterium bovis grew as visible colonies along the line of inoculation. However, due to long-term storage in conditions of low temperature (3°C) morphology of mycobacteria differed significantly from initial cultures formed by rod-shaped bacteria. Some of them became pigment-forming and smooth on the surface. Unlike the initial strain of mycobacteria, a perennial bacteria stored under hard conditions did not cause the death of guinea pigs or their sensitization to a purified protein derivative for mammals. Morphological forms of the perennial mycobacteria had the following changes: pigment forming, L-forms of the vesicular type, non-acid-fast thread-like (filamentous) bacillary forms, and elementary bodies when compared to the initial strain. There were also some genetic changes in the target DNA due to the long-term storage of M. bovis. It may indicate a mutation in the pathogen's DNA. These mycobacteria had altered biochemical activity during storage. The number of passages on the solid nutrient medium did not affect their fermentative activity. However, the low cultivation temperature increases mycobacterial catalase activity and the ability to hydrolyze Tween-80.