Siouxsie Wiles (University of Auckland) and her team have modified Mycobacterium tuberculosis (which causes TB) to produce light. The scientists treat mice with the modified bacteria, then track the course of infection by measuring how much light is emitted from the mouse. These mice (M1–M4) have living Mycobacterium in their lungs. Note that the image has been artificially coloured to show how much light is emitted (red is the strongest light emission and blue is the weakest).