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 It is intuitively obvious that, when testing the effectiveness of an antibiotic or antimicrobial compound, noninvasive imaging methods for tracking the progress or retreat of the invading microorganism in vivo and in situ would be invaluable. Researchers Ming Zhao and colleagues at the Massachusetts Institute of Technology (Cambridge, MA) and the Department of Surgery, University of California, San Diego, reported on such a new method involving the use of a green fluorescent protein (GFP)-expressing system (Proc. Natl. Acad. Sci. U.S.A. 2001, 98, 9814–9818). Having previously determined that they could follow the development and metastasis of GFP-transformed tumor cells in mice using whole-body imaging, the researchers decided to follow the behavior of GFP-expressing E. coli in four-week-old nude mice in situ.The bacteria were introduced by either injection, enema, or gavage (esophageal catheterization).
After gavage, the bacteria were clearly visible as they progressed from stomach to small intestine and then colon.The noninvasive imaging proved comparable to imaging performed on animals whose abdominal cavities were surgically exposed. Peritoneal infection with the E. coli could be followed in the absence and presence of an antibiotic—in this case, kanamycin. In untreated animals, the fluorescent E. coli could be followed as they percolated throughout the body, leading to death within 6 h. In treated animals, the fluorescence remained localized and the animals survived.
The possible uses of this technique for following the progress of bacterial infection and the effects of treatment appear promising. The process should also allow researchers to better determine the tissue specificity of infection and the spatial migration of the infectious agents. Previous attempts by other researchers at such whole-body imaging using the luciferin–luciferase bioluminescence system were far less sensitive than the more brilliantly illuminating GFP, and they required the use of intrusive procedures to trigger light production.
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