Monitoring Tuberculosis Drug Activity in Live Animals by Using Near-Infrared Fluorescence Imaging

Worldwide, tuberculosis (TB) is the leading cause of death due to infection with a single pathogenic agent, Mycobacterium tuberculosis. In the absence of an effective vaccine, new, more powerful antibiotics are required to halt the growing spread of multidrug-resistant strains and to shorten the duration of TB treatment. However, assessing drug efficacy at the preclinical stage remains a long and fastidious procedure that delays the progression of drugs down the pipeline and towards the clinic. In this investigation, we report the construction, optimization, and characterization of genetically engineered near-infrared (NIR) fluorescent reporter strains of the pathogens Mycobacterium marinum and Mycobacterium tuberculosis that enable the direct visualization of bacteria in infected zebrafish and mice, respectively. Fluorescence could be measured precisely in infected immunodeficient mice, while its intensity appeared to be below the limit of detection in immunocompetent mice, probably because of the lower bacterial load obtained in these animals. Furthermore, we show that the fluorescence level accurately reflects the bacterial load, as determined by CFU enumeration, thus enabling the efficacy of antibiotic treatment to be assessed in live animals in real time. The NIR fluorescent imaging system disclosed here is a valuable resource for TB research and can serve to accelerate drug development.