Background: Aspergillus fumigatus is a ubiquitous saprophytic airborne fungus responsible for more than one million deaths every year. The
siderophores of A. fumigatus represent important
virulence factors that contribute to the microbiome-metabolome dialog in a host. From a diagnostic point of view, the monitoring of Aspergillus secondary metabolites in urine of a host is promising due to the non-invasiveness, rapidity, sensitivity, and potential for standardization. Methods: Using a model of experimental
aspergillosis in immunocompromised Lewis rats, the fungal
siderophores ferricrocin (FC) and
triacetylfusarinine C (TAFC) were monitored in rat urine before and after lung inoculation with A. fumigatus conidia. Molecular
biomarkers in high-dose (HD) and low-dose (LD)
infection models were separated using high performance liquid chromatography (HPLC) and were detected by mass spectrometry (MS). In the current work, we corroborated the in vivo MS
infection kinetics data with micro-positron emission tomography/computed tomography (μPET/CT) kinetics utilizing 68Ga-labeled TAFC. Results: In the HD model, the initial FC signal reflecting
aspergillosis appeared as early as 4 h post-
infection. The results from seven
biological replicates showed exponentially increasing metabolite profiles over time. In A. fumigatus, TAFC was found to be a less produced
biomarker that exhibited a kinetic profile identical to that of FC. The amount of
siderophores contributed by the inoculating conidia was negligible and undetectable in the HD and LD models, respectively. In the μPET/CT scans, the first detectable signal in HD model was recorded 48 h post-
infection. Regarding the MS assay, among nine
biological replicates in the LD model, three animals did not develop any
infection, while one animal experienced an exponential increase of metabolites and died on day 6 post-
infection. All remaining animals had constant or random FC levels and exhibited few or no symptoms to the experiment termination. In the LD model, the TAFC concentration was not statistically significant, while the μPET/CT scan was positive as early
as 6 days post-
infection. Conclusion:
Siderophore detection in rat urine by MS represents an early and non-invasive tool for diagnosing
aspergillosis caused by A. fumigatus. μPET/CT imaging further determines the
infection location in vivo and allows the visualization of the
infection progression over time.