The Enterobacteriaceae are a family of rod-shaped Gram-negative bacteria that normally inhabit the gastrointestinal tract and are the most common cause of Gram-negative bacterial infections in humans. In addition to causing serious multidrug-resistant, hospital-acquired infections, a number of Enterobacteriaceae species are also recognized as biothreat pathogens. As a consequence, new tools are urgently needed to specifically identify and localize infections due to Enterobacteriaceae and to monitor antimicrobial efficacy. In this report, we used commercially available 2-[18F]-fluorodeoxyglucose (18F-FDG) to produce 2-[18F]-fluorodeoxysorbitol (18F-FDS), a radioactive probe for Enterobacteriaceae, in 30 min. 18F-FDS selectively accumulated in Enterobacteriaceae, but not in Gram-positive bacteria or healthy mammalian or cancer cells in vitro. In a murine myositis model, 18F-FDS positron emission tomography (PET) rapidly differentiated true infection from sterile inflammation with a limit of detection of 6.2 ± 0.2 log10 colony-forming units (CFU) for Escherichia coli. Our findings were extended to models of mixed Gram-positive and Gram-negative thigh co-infections, brain infection, Klebsiella pneumonia, and mice undergoing immunosuppressive chemotherapy. This technique rapidly and specifically localized infections due to Enterobacteriaceae, providing a three-dimensional holistic view within the animal. Last, 18F-FDS PET monitored the efficacy of antimicrobial treatment, demonstrating a PET signal proportionate to the bacterial burden. Therapeutic failures associated with multidrug-resistant, extended-spectrum β-lactamase (ESBL)–producing E. coli infections were detected in real time. Together, these data show that 18F-FDS is a candidate imaging probe for translation to human clinical cases of known or suspected infections owing to Enterobacteriaceae.

The modern patient is increasingly susceptible to bacterial infections including those due to multi-drug resistant organisms (MDROs). Noninvasive whole-body analysis with pathogen-specific imaging technologies can significantly improve patient outcomes by rapidly identifying a source of infection and monitoring the response to treatment, but no such technology exists clinically. Methods We systematically screened 961 random, radiolabeled molecules in silico as substrates for essential metabolic pathways in bacteria, followed by in vitro uptake in representative bacteria – Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and mycobacteria. Fluorine-labeled analogs, that could be developed as positron emission tomography (PET)-based imaging tracers, were evaluated in a murine myositis model. Results We identified three novel, non-toxic molecules demonstrating selective bacterial uptake: para-aminobenzoic acid (PABA), with uptake in all representative bacteria including Mycobacterium tuberculosis; mannitol, with selectively uptake in S. aureus and E. coli; and sorbitol, accumulating only in E. coli. None accumulated in mammalian cells or heat-killed bacteria, suggesting metabolism-derived specificity. In addition to an extended bacterial panel of laboratory strains, all three molecules rapidly accumulated in respective clinical isolates of interest including MDROs such as methicillin resistant S. aureus (MRSA), extended-spectrum beta-lactamase (ESBL)-producing, and carbapenem-resistant Enterobacteriaceae. In a murine myositis model, fluorine-labeled analogs of all three molecules could rapidly detect and differentiate infection sites from sterile inflammation in mice (P=0.03). Finally, 2-deoxy-2-[F-18]fluoro-D-sorbitol (18F-FDS) can be easily synthesized from 2-deoxy-2-[F-18]fluoro-D-glucose (18F-FDG). PET, utilizing 18F-FDS synthesized using current good manufacturing practice, could rapidly differentiate true infection from sterile inflammation to selectively localize E. coli infection in mice. Conclusion We have developed a systematic approach that exploits unique biochemical pathways in bacteria to develop novel pathogen-specific imaging tracers. These tracers have significant potential for clinical translation to specifically detect and localize a broad range of bacteria, including MDROs.

Central nervous system (CNS) tuberculosis (TB) is the most severe form of extra-pulmonary TB and disproportionately affects young children where the developing brain has a unique host response. New Zealand white rabbits were infected with Mycobacterium tuberculosis via subarachnoid inoculation at postnatal day 4-8 and evaluated until 4-6 weeks post-infection. Control and infected rabbit kits were assessed for the development of neurological deficits, bacterial burden, and postmortem microbiologic and pathologic changes. The presence of meningitis and tuberculomas was demonstrated histologically and by in vivo magnetic resonance imaging (MRI). The extent of microglial activation was quantified by in vitro immunohistochemistry as well as non-invasive in vivo imaging of activated microglia/macrophages with positron emission tomography (PET). Subarachnoid infection induced characteristic leptomeningeal and perivascular inflammation and TB lesions with central necrosis, a cellular rim and numerous bacilli on pathologic examination. Meningeal and rim enhancement was visible on MRI. An intense microglial activation was noted in M. tuberculosis-infected animals in the white matter and around the TB lesions, as evidenced by a significant increase in uptake of the tracer 124I-DPA-713, which is specific for activated microglia/macrophages, and confirmed by quantification of Iba-1 immunohistochemistry. Neurobehavioral analyses demonstrated signs similar to those noted in children with delayed maturation and development of neurological deficits resulting in significantly worse composite behavior scores in M. tuberculosis-infected animals. We have established a rabbit model that mimics features of TB meningitis in young children. This model could provide a platform for evaluating novel therapies, including host-directed therapies, against TB meningitis relevant to a young child's developing brain.