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Abstract
Positron emission tomography (PET) with fluorine-18-fluorodeoxyglucose (18F-FDG) can be applied to detect infection and inflammation. However, it was so far not known to what extent bacterial pathogens may contribute to the PET signal. Therefore, we investigated whether clinical isolates of frequently encountered bacterial pathogens take up 18F-FDG in vitro, and whether FDG inhibits bacterial growth as previously shown for 2-deoxy-glucose. 22 isolates of Gram-positive and Gram-negative bacterial pathogens implicated in fever and inflammation were incubated with 18F-FDG and uptake of 18F-FDG was assessed by gamma-counting and µPET imaging. Possible growth inhibition by FDG was assayed with Staphylococcus aureus and the Gram-positive model bacterium Bacillus subtilis. The results show that all tested isolates accumulated 18F-FDG actively. Further, 18F-FDG uptake was hampered in B. subtilis pts mutants impaired in glucose uptake. FDG inhibited growth of S. aureus and B. subtilis only to minor extents, and this effect was abrogated by pts mutations in B. subtilis. These observations imply that bacteria may contribute to the signals observed in FDG-PET infection imaging in vivo. Active bacterial FDG uptake is corroborated by the fact that the B. subtilis phosphotransferase system is needed for 18F-FDG uptake, while pts mutations protect against growth inhibition by FDG.
Highlights
For 18F-FDG uptake studies, Streptococcus pneumoniae, Enterococcus faecalis and Enterococcus faecium were cultured in brain-heart infusion (BHI), while all other bacteria were cultured in tryptic soy broth (TSB)
FDG, a range of different Gram-positive and Gram-negative bacteria including mostly clinical isolates were incubated with 18F-FDG, and uptake was determined with a calibrated gamma-counter
The 18F-FDG Positron emission tomography (PET) signals were quantified and the absorbed activity per colony forming units (CFUs) was determined as shown in Fig. 1(A and B)
Summary
FDG inhibited growth of S. aureus and B. subtilis only to minor extents, and this effect was abrogated by pts mutations in B. subtilis These observations imply that bacteria may contribute to the signals observed in FDG-PET infection imaging in vivo. Due to increasingly ageing populations, higher rates of organ transplantations and expanding possibilities for chemotherapy, the numbers of immune-compromised patients who are at risk of bacterial infections are steadily increasing This problem is exacerbated by increased use of implanted biomaterials and medical devices, which are susceptible to bacterial contaminations and infection[1]. There is always a risk of contaminations by other bacteria not related to the actual infection resulting in false-positive culture outcomes Since these challenges often lead to blind management of bacterial infections, there is an urgent need for diagnostic tools that allow real-time detection of infecting bacteria in the patient, for example by infection imaging[1, 4, 5].
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