Abstract

Experimental microbial therapies, e.g. compassionate clinical use of phage or fecal microbiota transplantation after antibiotic failure, have been introduced to treat diseases associated with dysbiosis. However, little is known about where therapeutic microbes disseminate after their delivery; how long they persist in the body; and what effect these microorganisms have on permeability of the gut membrane. Currently, most microbiota analyses are conducted ex vivo, risking sample contamination or changes in microbial composition. To address these shortcomings, we are using simultaneous positron emission tomography/magnetic resonance imaging (PET/MRI) for in vivo assessment of bacterial migration, engraftment, and gut permeability. We hypothesize that 89Zr-labelled microbiota permits long-term cell tracking by PET/MRI throughout the gastrointestinal tract and beyond.
To radiolabel cell surface protein on either bacteria or bacteriophage, a universal strategy was adopted employing 89Zr (half-life 78.4 hours) chelated to a bifunctional desferrioxamine derivative that covalently binds primary amines through a p-isothiocyanato-benzyl linkage (89Zr-DBN). To expedite translation to human study, the pig provides a suitable large animal model of gut physiology and imaging on a clinical scale. Here, real-time measures of 89Zr-labelled bacteria and bacteriophage dissemination are presented, with validation from the analysis of post-mortem tissue by PCR, digital autoradiography, and histological staining. The biodistribution of radiotracer(s) and associated dosimetry are assessed using Health Canada approved OLINDA software (Hermes). Molecular imaging with simultaneous PET/MRI enables in vivo tracking of 89Zr-labelled bacteria and bacteriophage; provides the means to assess distribution and retention of microorganisms; and is important for widespread acceptance and implementation of microbial therapies.