Optical imaging of bacterial infection in living mice using a fluorescent near-infrared molecular probe

Abstract

An optical imaging probe was synthesized by attaching a near-infrared carbocyanine fluorophore to an affinity group containing two zinc(II) dipicolylamine (Zn-DPA) units. The probe has a strong and selective affinity for the surfaces of bacteria, and it was used to image infections of Gram-positive S. aureus and Gram-negative E. coli bacteria in living nude mice. After intravenous injection, the probe selectively accumulates at the sites of localized bacterial infections in the thigh muscles of the mice.

Figure 1

Left: Phase contrast image of S. aureus cells treated with probe 1 (10 μM) and viewed at 1500X. Middle: Fluoresence image of the same cells acquired with a Cy7 filter set. Right: Fluorescence image of a live mouse after thigh muscle injections of S. aureus cells that were pre-incubated for 5 min with 10 μM of either 1 or 2 (left and right leg, respectively). Scale represents relative fluorescence intensity in arbitrary units.

Figure 2

Optical images of a mouse with a S. aureus infection in the left rear thigh muscle. Images were acquired before (A), and immediately following (B), intravenous injection of probe 1, and at 6 h (C), 12 h (D), 18 h (E), and 21 h (F). Scale represents the same relative fluorescence intensity for all six images in arbitrary units.