Is Imaging Bacteria with PET a Realistic Option or an Illusion?

The application of [(18)F]-fluorodeoxyglucose ([(18)F]FDG) as a radiotracer to detect sites of inflammation (either due to bacterial infection or primary inflammation) has led to exploring the role of PET in visualizing bacteria directly at sites of infection. However, the results from such efforts are controversial and inconclusive so far. We aimed to assess the limitations of PET as an effective modality in the diagnosis of bacterial infections. Inflammation due to bacterial infections can be visualized by using [(18)F]FDG-PET. However, the non-specificity of [(18)F]FDG makes it undesirable to visualize bacteria as the underlying cause of inflammation. Hence, more specific radiotracers that possibly bind to or accumulate in bacteria-specific receptors or enzymes are being explored. Several radiotracers, including 2-deoxy-2-[(18)F]fluorosorbitol ([(18)F]FDS), 6-[(18)F]-fluoromaltose, [(11)C]para-aminobenzoic acid ([(11)C]PABA), radiolabeled trimethoprim ((11)C-TMP) and its analog fluoropropyl-trimethoprim ((18)F-FPTMP), other radiolabeled sugars, and antimicrobial drugs have been used to image microorganisms. Unfortunately, no progress has been made in translating the results to routine human use; feasibility and other factors have constrained their success in clinical settings. In the current article, we discuss the limitations of direct bacterial visualization with PET tracers, but emphasize the important role of [(18)F]FDG-PET as the only option for detecting evidence of infection.