Real-Time <i>in Vivo</i> Bacterial Imaging by Computed Tomography and Fluorescence Using Phage-Gold Nanorod Bioconjugates as Contrast Agents

Real-time <i>in vivo</i> imaging of bacterial infections is an important goal to aid the study and treatment of bacterial infections. Phages can be genetically engineered to ensure a particular biomolecular target specificity, and gold nanomaterials can be conjugated to phages for a variety of applications including biosensing. In this paper, we describe methods to use phage-gold nanorod conjugates for <i>in vivo</i> detection and imaging of the bacterial species <i>Pseudomonas aeruginosa</i> in mice. The imaging modalities are computed tomography (CT), using gold as a contrast agent, and fluorescence, which can be applied when the FDA-approved near-infrared (NIR) dye indocyanine green (ICG) is also chemically cross-linked to the bioconjugates. In addition, rapid protocols for validating bioconjugate synthesis and the initial assessment of toxicity are given. In this example, the phage-gold nanorod probe is shown to specifically highlight <i>P. aeruginosa</i> without cross-reactivity to another Gram-negative organism (<i>V. cholerae</i>) <i>in vivo</i> and appears to be biocompatible. Phage-directed imaging probes may thus be useful for the characterization and diagnosis of bacterial infections.