[Quantitative analysis of mRNA as a marker for viability of Mycobacterium tuberculosis].

Objective: To study whether quantitative analysis of M. tuberculosis mRNA could be used to assess bacterial viability.

Methods: The levels of M. tuberculosis mRNA were compared 24, 48, and 72 hours after M. tuberculosis H(37)R(V) was treated with no drug, 1.0 micro g/ml and 10.0 micro g/ml rifampicin, 0.2 micro g/ml and 1.0 micro g/ml isoniazid, 2 micro g/ml and 4 micro g/ml ethambutol, 2 micro g/ml and 4 micro g/ml streptomycin, 1.25 micro g/ml and 5.00 micro g/ml ofloxacin. The levels of mRNA were determined by quantitative PCR.

Results: After exposure to isoniazid, rifampicin, and streptomycin for 24 h, the level of M. tuberculosis H(37)R(V) was reduced markedly. Similarly, after exposure to isoniazid, streptomycin, ethambutol, and ofloxacin for 72 h, the level of M. tuberculosis H(37)R(V) was identical, but higher than that after exposure to rifampicin. Exposure of M. tuberculosis H(37)R(V) to rifampicin for 24 h reduced the levels of 85B mRNA to 0.02% of the control; exposure to other drugs for 24 h reduced the levels to 1% approximately 10% of the control, and for 72 h to less than 1% of the control.

Conclusions: The levels of mRNA can show the difference between M. tuberculosis H(37)R(V) exposed and unexposed to drugs, and are consistent with colony forming unit. mRNA could be used as a marker for assessing the viability of M. tuberculosis.