Fluorescent Molecular Probe for In Vivo Targeting and Live Cell Imaging of Intracellular Pathogenic E. coli

Intracellular bacterial infections are difficult to diagnose and treat because the host cells shelter the bacteria from molecular recognition by imaging agents, antibiotics, and the immune system. This problem arises when bladder epithelial cells are infected by uropathogenic Escherichia coli (UPEC)—one of the causative agents of urinary tract infection (UTI). UTIs are among the most common bacterial infections and a worldwide health concern. It is challenging to design molecular probes for intracellular UPEC imaging or targeted antibiotic treatment because the probe must possess multiple capabilities—it must permeate the host cell plasma membrane and selectively associate with the intracellular UPEC. Here, we report a “first-in-class” fluorescent probe called BactVue that is comprised of two structural components: a modified zinc (II)-2,2’-dipicolylamine complex (Zn-Oxy-DPA) as the bacteria targeting unit and an appended near-infrared cyanine fluorophore that is hydrophilic but with near-neutral electrostatic charge. The unique capacity of BactVue to target intracellular UPEC was demonstrated by a series of in vitro and in vivo fluorescence imaging studies. The results show that BactVue can penetrate infected human bladder epithelial cells and stain intracellular UPEC both in vitro and in a mouse model of UTI. These results support the feasibility of incorporating BactVue into diagnostic near-infrared fluorescence imaging methods that visualize the location of infected bladder cells during active UTI. There is also great potential to develop homologous molecular probes for other imaging modalities and to design new therapeutic approaches that exploit selective targeting by the Zn-Oxy-DPA unit.