Abstract: The invention relates to a non-invasive imaging method of bacteria. One embodiment comprises labeling the bacteria with a radioisotope, then delivering it to the gut of a human or animal. Another embodiment is to label bacteriophages, then administer them to a human or animal, so that they infect (and thus co-localize with) bacteria already resident in the human or animal. The bacteriophage can then be imaged, showing the location of the resident bacteria of interest. In another embodiment, the invention is related more generally to the labelling of bacteria or bacteriophages with a radio-metal or radioisotope to render the labeled gut bacteria and the bacteria in the body visible to nuclear medicine PET and SPECT imaging guided by functional/structural MRI and/or CT imaging.