To improve bioluminescence imaging, hairs were removed [37] . We observed the mice to detect clinical signs due to the infection prior to imaging. Mice that exhibited no severe clinical signs were anesthetized and injected i.p. with 100 mL h-coelenterazine (1 mg/ml). The h-coelenterazine stock solution provided by Nanolight Technology (Pinetop, AZ) was solubilized in ethanol-propylene glycol solution (1:1) at 10 mg/ml. This solution was diluted in PBS (1:9) just before imaging. The h-coelenterazinetreated mice were immediately placed in a hermetically sealed light-tight-transparent chamber (TEM Sega, Lormont, France) equipped with two HEPA filters. One HEPA filter was connected to an air pump, thus allowing air renewal during the imaging. The bio containment chamber allowed simultaneous imaging of 6 mice. The mice were imaged 15 and 20 min after h-coelenterazine injection for the whole body and the thorax, respectively [38] . Imaging was performed with a Xenogen's IVIS 100 system, including a cooled charge-coupled device (CCD) camera [39, 40] . Integration periods ranged from 0.5 to 120 s depending on the amounts of light emitted at various infection sites. Images were obtained using Living ImageH 3.1 software (Xenogen, Alameda, CA). Specific regions of interest (ROI) on the images were defined without overlay, using the anatomic location of the different organs and their visual observation through the skin when possible. For each imaging session, a mock-infected mouse was used as a negative control. A signal was considered significant if its intensity in infected mice was at least twofold higher than the background luminescence in the mock-infected mouse. After the last imaging time point, mice were euthanized.