Effect of low temperature on growth, viability, and synthesis of mycolic acids of Mycobacterium tuberculosis strain H37Ra.

Cultures of Mycobacterium tuberculosis strain H37Ra were grownto early logarithmic phase at 37 degrees C and were incubated at 16 degrees, 20 degrees, and 25 degrees C. The decrease in this ability was more rapid at 20 degrees C than at 16 degrees C. Low-temperature incubation caused decreases in the ratios of mycolic acids and monounsaturated C16-19 fatty acids relative to the total of fatty acids synthesized. It also caused an increase in the ratio of saturated C24-26 fatty acids relative to the total of fatty acids synthesized. These ratios were based on the incorporation of radiolabel from 14C-acetate into fatty acids. These results showed that when M. tuberculosis H37Ra was incubated at low temperatures, it did not adapt by increasing the ratio of unsaturated to saturated fatty acids synthesized. The ability of the cells to synthesize mycolic acids was sharply decreased. These changes may lead to the loss of viability of M. tuberculosos H37Ra. Mycolic acid synthesis is similarly affected by exposure of cells to isoniazid, an antimycobacterial drug.