Stress and Host Immunity Amplify Mycobacterium tuberculosis Phenotypic Heterogeneity and Induce Nongrowing Metabolically Active Forms

Giulia Manina, Neeraj Dhar, and John D. McKinney

Cell Host & Microbe Vol.17 (32–46), Jan. 14, 2015

Speaker: Meng-Ju Tsai (蔡孟儒)                                                  Time: 13:00~14:00, Jun. 24, 2015

Commentator: Dr. Ching-Hao Teng (鄧景浩 老師)               Place: Room 601

Abstract:

    Mycobacterium tuberculosis (Mtb), which causes tuberculosis , has been infecting one-third of population in the world. A characteristic of Mtb infection is a clinical change from an acute disease to latent state [1]. In the infected mouse, an animal model, it was observed that Mtb in lungs exhibited exponential growth in the acute stage and then markedly slow growth in the latent phase [2]. However, the metabolic and replication states of Mtb in this transition of growth is not clear. Some studies suggested that the microbial pathogens may utilize the cell-to-cell phenotypic variation to evade host immunity and tolerate antimicrobial assults, allowing them to establish diverse colonization from acute to latent phase [3]. To test whether Mtb may use similar strategy, the authors employed the quantitative time-lapse microscopy and a fluorescent reporter, rRNA-GFP_des, to measure the single-cell metabolic activity in vitro and in vivo. They found a rapid decrease in rRNA-GFP_des fluorescence followed by quiescent growth when Mtb was transferred from rich medium to PBS, but the reverse was observed only in a small fraction of population when the bacteria was transferred from PBS back to rich medium. They also observed a slow decrease of rRNA-GFP_des fluorescence during isoniazid (INH) exposure, and a subpopulation of bacteria survive after INH withdrawal. The intracellular bacteria in an infected macrophage showed increased phenotypic variation compared to those growing in vitro, but when the infected macrophage was treated with INH, the rRNA-GFP_des fluorescence of all bacteria decreased rapidly. In a normal mouse, the infecting Mtb in the lungs multiplied rapidly in early stage and then ceased to grow. However, the Mtbinfecting an IFN-γ^-/- mouse, which lost the key cytokine in anti-Mtb immunity, multiplied in the lungs and then remained high number over time. Interestingly, there was a subpopulation of bacteria that maintained high rRNA-GFP_des fluorescence with non-resumed growth, called the nongrowing but metabolically active (NGMA) bacteria, in those recovered from the lungs of latent infection or transferred from nutrient-limited medium to permissive condition. In conclusion, Mtb undergoes increased phenotyptic heterogeneity when subjected to various stresses, like starvation, host immune attack and drug treatment, and NGMA bacteria may be a key population retaining the ability to survive the stresses

References:

1. E.S. Rittershaus et al. (2013) The normalcy of dormancy: common themes in microbial quiescence. Cell Host & Microbe, 13, pp. 643–651
2. Muñoz-Elías et al. (2005) Replication dynamics of Mycobacterium tuberculosis in chronically infected mice. Infect. Immun., 73, pp. 546–551
3. N.R. Cohen et al. (2013) Microbial persistence and the road to drug resistance. Cell Host & Microbe, 13, pp. 632–642