[Susceptibility test to rifampin by using quantitative analysis of Mycobacterium tuberculosis mRNA].

Objective: To evaluate the significance of quantitative analysis of Mycobacterium tuberculosis mRNA in the test of susceptibility of Mycobacterium tuberculosis strains to rifampin.

Methods: The susceptibility to rifampin of fifty-three clinical isolated strains was test by the percentage of Mycobacterium tuberculosis 85B mRNA copies before and after the use of rifampin, and 1% and 10% were used as the standards for drug resistance, which was compared with the absolute concentration method. Among them, 29 were rifampin resistant strains and 24 rifampin sensitive strains.

Results: When the concentration of rifampin was 1 micro g/ml, and 1% and 10% were used as the standards, the accuracy of quantitative analysis of Mycobacterium tuberculosis mRNA with the absolute concentration method was 70% and 81% respectively, and the sensitivity of quantitative analysis of Mycobacterium tuberculosis mRNA was 100% and 100% respectively, while the specificity of quantitative analysis of Mycobacterium tuberculosis mRNA was 33% and 58%. When the concentration of rifampin was 2 micro g/ml, the accuracy of quantitative analysis of mRNA with the absolute concentration method was 85% and 93% respectively, and the sensitivity was 100% and 97% respectively, while the specificity was 67% and 88% respectively. When the concentration of rifampin was 4 micro g/ml, the accuracy was 93% and 93%, and the sensitivity was 93% and 93%, while the specificity was 92% and 92%.

Conclusions: Quantitative analysis of Mycobacterium tuberculosis mRNA was a rapid, sensitive method in rifampin resistance screening. We suggest that the critical concentration of rifampin be 2 micro g/ml, and the critical proportion of mRNA copy be 10%.