Scedosporium and Lomentospora: an updated overview of underrated opportunists

Analysis of Microbial Siderophores by Mass Spectrometry

Siderophores represent important microbial virulence factors and infection biomarkers. Their monitoring in fermentation broths, bodily fluids, and tissues should be reproducible. Similar isolation, characterization, and quantitation studies can often have conflicting results, and without proper documentation of sample collection, data processing, and analysis methods, it is difficult to reexamine the data and reconcile these differences. In this Springer Nature Protocol, we present the procedure optimized for ferricrocin/triacetylfusarinine C extraction from biological material as well as for tissue fixation and cryosectioning for optical microscopy and for both elemental and molecular mass spectrometry imaging. Special attention is paid to siderophore data mining from conventional and product ion mass spectra, liquid chromatography, and mass spectrometry imaging datasets, performed here by our free software called CycloBranch.

Early and Non-invasive Diagnosis of Aspergillosis Revealed by Infection Kinetics Monitored in a Rat Model

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.

Surface properties, adhesion and biofilm formation on different surfaces by Scedosporium spp. and Lomentospora prolificans

In the present work, some surface properties of the fungi Scedosporium apiospermum, S. aurantiacum, S. minutisporum, and Lomentospora prolificans and their capability to adhere to and form a biofilm on diverse surfaces were evaluated. All four species had high conidial surface hydrophobicity and elevated electronegative zeta potentials. Abundant quantities of melanin were detected at the conidial surface, whereas sialic acid was absent. The numbers of non-germinated and germinated conidia adhered to poly-L-lysine-covered slides was higher than on glass after 4 h of fungi-surface contact. Additionally, after 72 h of interaction a typical biofilm structure had formed. Mature biofilms were also observed after 72 h on a nasogastric catheter (made from polyvinyl chloride), a late bladder catheter (siliconized latex), and a nasoenteric catheter (polyurethane). Interestingly, biofilm biomass increased considerably when the catheters had previously been incubated with serum. These results confirm that Scedosporium/Lomentospora spp. are capable of forming biofilms on diverse abiotic surfaces.

Identification of 14-α-Lanosterol Demethylase (CYP51) in Scedosporium Species

Scedosporium spp. cause infections (scedosporiosis) in both immunocompetent and immunocompromised individuals and may persistently colonize the respiratory tract in patients with cystic fibrosis (CF). They are less susceptible against azoles than are other molds, such as Aspergillus spp., suggesting the presence of resistance mechanisms. It can be hypothesized that the decreased susceptibility of Scedosporium spp. to azoles is also CYP51 dependent. Analysis of the Scedosporium apiospermum and Scedosporiumaurantiacum genomes revealed one CYP51 gene encoding the 14-α-lanosterol demethylase. This gene from 159 clinical or environmental Scedosporium isolates and three Lomentospora prolificans isolates has been sequenced and analyzed. The Scedosporium CYP51 protein clustered with the group of known CYP51B orthologues and showed species-specific polymorphisms. A tandem repeat in the 5' upstream region of Scedosporium CYP51 like that in Aspergillus fumigatus could not be detected. Species-specific amino acid alterations in CYP51 of Scedosporium boydii, Scedosporiumellipsoideum, Scedosporium dehoogii, and Scedosporiumminutisporum isolates were located at positions that have not been described as having an impact on azole susceptibility. In contrast, two of the three Sapiospermum-specific amino acid changes (Y136F and G464S) corresponded to respective mutations in A. fumigatus CYP51A at amino acid positions 121 and 448 (Y121F and G448S, respectively) that had been linked to azole resistance.

Varying susceptibility of clinical and environmental Scedosporium isolates to chemical oxidative stress in conidial germination

Scedosporium species are opportunistic pathogens causing a great variety of infections in both immunocompetent and immunocompromised individuals. The Scedosporium genus ranks the second among the filamentous fungi colonizing the airways of patients with cystic fibrosis (CF), after Aspergillus fumigatus, and most species are capable to chronically colonize the respiratory tract of these patients. Nevertheless, few data are available regarding evasion of the inhaled conidia to the host immune response. Upon microbial infection, macrophages and neutrophils release reactive oxygen species (ROS). To colonize the respiratory tract, the conidia need to germinate despite the oxidative stress generated by phagocytic cells. Germination of spores from different clinical or environmental isolates of the major Scedosporium species was investigated in oxidative stress conditions. All tested species showed susceptibility to oxidative stress. However, when comparing clinical and environmental isolates, differences in germination capabilities under oxidative stress conditions were seen between species as well as within each species. Among environmental isolates, Scedosporium aurantiacum isolates were the most resistant to oxidative stress whereas Scedosporium dehoogii were the most susceptible. Overall, the differences observed between Scedosporium species in the capacity to germinate under oxidative stress conditions could explain their varying prevalence and pathogenicity.