In vivo optical imaging of bacterial infection and antibiotic response in intact nude mice

Abstract

We describe imaging the luminance of red fluorescent protein (DsRed₂)-expressing bacteria from outside intact infected animals. This simple, nonintrusive technique can show in great detail the temporal behavior of the infectious process. Fluorescence stereo microscope, laser and cooled CCD are expensive to many institutes, we set up an inexpensive compact whole-body fluorescent imaging tool, which consisted of a digital camera, fluorescence filters and a mercury 50-W lamp power supply as excitation light source. The bacteria, expressing the DsRed₂, are sufficiently bright as to be clearly visible from outside the infected animal and recorded with simple equipment. Introduced bacteria were observed in the abdomen. Instantaneous real-time images of the infectious process were acquired by using a digital camera by simply illuminating nude mice with mercury lamp. The development of infection over 48 hours and its regression after kanamycin treatment were visualized by whole-body imaging. The DsRed₂ was excited directly by mercury lamp with EF500/50 nm band-pass filter and fluorescence was recorded by digital camera with CB580 nm long-pass filter. By this easy operation tool, the authors imaged, in real time, fluorescent tumors growing in live mice. The imaging system is external and noninvasive. For one year our experiments suggested the imaging scheme was feasible, which affords a powerful approach to visualizing the infection process.