[A study on in vitro and in vivo models of Mycobacterium tuberculosis persistence]

To establish in vivo and in vitro models of persistent Mycobacterium tuberculosis infection, and therefore to study the persisters in different conditions and periods of chemotherapy, and to explore the relationship between the persisters and chemotherapy.

The persisters in the two models were examined by culturing Mycobacterium tuberculosis in oxygen-starved condition and determining the mRNA expression of isocitrate lyase (ICL), alpha-crystallin chaperone (Acr) and 85B through quantitative PCR.

The bacteria which could be cultured in oxygen-starved condition were discovered in both models. The mRNA expression of ICL and Acr increased gradually and dramatically after culture for 4 days in the in vitro model, their values being (5.3 +/- 0.9) and (6.4 +/- 1.6) log copy/ml respectively. While the mRNA expression of 85B showed no significant change in oxygen-starved condition, it increased significantly in the standard condition, the values being (6.1 +/- 0.9) log copy/ml at 10th day. In the mice infected with Mycobacterium tuberculosis, the mRNA expression of ICL was detected in 2 and 4 weeks post-infection, and decreased 4 weeks after treatment. The Acr mRNA showed no or very low expression 4 weeks post-infection or 4 weeks after treatment, but it increased significantly 8 and 10 weeks after treatment, with a value of (6.2 +/- 1.7) log copy/ml at 10 weeks, and its expression was still detected 12 weeks after treatment and 4 weeks after the cessation of treatment [(3.0 +/- 1.6) log copy/ml]. The expression of 85B mRNA was high before the treatment [(6.4 +/- 1.1) log copy/ml], and decreased gradually during the therapy.

The models of in vitro and in vivo persistence of Mycobacterium tuberculosis were established. ICL and Acr mRNAs were highly expressed, which may be the markers of persisters. Persisters can be detected by culture in oxygen-starved conditions and the measurement of mRNA expression.