CDC PUBLIC HEALTH IMAGE LIBRARY, JANICE HANEY CARR
An new method to screen for active tuberculosis may soon provide faster and simpler detection after an international team of researchers optimized a strategy to make Mycobacterium tuberculosis fluoresce brightly under the microscope, according to research published online last month (January 25) in the Journal of Clinical Microbiology. Using fluorophages, bacteria viruses carrying a fluorescent reporter gene, the researchers infected mycobacteria in tuberculin sputum coughed up from patients’ lungs. Within hours, infected bacteria expressed the reporter and fluoresced at levels high enough to see under a fluorescence microscope (see video below for time-lapse demonstration).
Previous attempts to create a similar screen for tuberculosis bacteria suffered from low reporter expression. To address this issue, the researchers started with a bacteriophage plasmid with enhanced cloning capacity and added a strong phage promoter. This produces a fluorescent signal 100-fold greater than any previously reported, and mycobacteria-positive clinical samples were detected via microscope without any need for culturing the bacteria. Additionally, the technology lends itself to drug resistance screening. In the presence of antibiotics, drug resistant bacteria continue to glow, while drug sensitive bacteria cannot express the reporter gene.