Technetium-99m labelled fluconazole and antimicrobial peptides for imaging of Candida albicans and Aspergillus fumigatus infections

The aim of this study was to investigate whether technetium-99m labelled fluconazole can distinguish fungal from bacterial infections. Fluconazole was labelled with Tc-99m and radiochemical analysis showed less than 5% impurities. The labelling solution was injected into animals with experimental infections. For comparison. we used two peptides for infection detection, i.e. UBI 29-41 and hLF 1-11, and human IgG, all labelled with Tc-99m. Mice were infected with Candida albicans or injected with heat-killed C. albicans or lipopolysaccharides to induce sterile inflammation. Also, mice were infected with Staphylococcus aureus or Klebsiella pneumoniae. Next. accumulation of Tc-99m-fluconazole and Tc-99m-labelled peptides/IgG at affected sites was determined scintigraphically. Tc-99m-fluconazole detected C. albicans infections (T/NT ratio=3.6 +/- 0.47) without visualising bacterial infections (T/NT ratio=1.3 +/- 0.04) or sterile inflammatory processes (heat-killed C. albicans: T/NT ratio=1.3 +/- 0.2 lipopolysaccharide: T/NT ratio=1.4 +/- 0.1). C. albicans infections were already seen within the first hour after injection of Tc-99m-fluconazole (T/NT ratio=3.1 +/- 0.2). A good correlation (R-2=0.864, P<0.05) between T/NT ratios for this tracer and the number of viable C. albicans was found. Although Tc-99m-UBI 29-41 and Tc-99m-hLF 1-11 were able to distinguish C. albicans infections from sterile inflammatory processes in mice, these Tc-99m-labelled peptides did not distinguish these fungal infections from bacterial infections. It is concluded that Tc-99m-fluconazole distinguishes infections with C. albicans from bacterial infections and sterile inflammations.