Bloodstream infections caused by Magnusiomyces capitatus and Magnusiomyces clavatus: epidemiological, clinical and microbiological features of two emerging yeast species.
Magnusiomyces clavatus and Magnusiomyces capitatus are emerging fungal pathogens with intrinsic resistance to many commonly used antifungal agents. While identification of both species is difficult, determination of susceptibility patterns is equally challenging with both commercially available and reference methods. For this reason, few data on invasive infections by Magnusiomyces spp. is available.
Objectives: to determine the epidemiology and susceptibility of Magnusiomyces isolates from bloodstream infections in Germany.
Methods: 35 Magnusiomyces isolates from bloodstream infections were identified by ITS sequencing and MALDI-TOF MS, growth characteristics were assessed on different media. Antifungal susceptibility was determined by EUCAST broth microdilution and gradient tests.
Results: Of the 35 isolates, M. clavatus was more common (N=25) compared to M. capitatus (N=10). Bloodstream infections by Magnusiomyces spp. were more common in men (61.8%) and most occurred in patients with haematological or oncological malignancies (79.4%). The highest antifungal activity against M. clavatus/M. capitatus was observed for voriconazole (MIC50 0.03/0.25 mg/L), followed by posaconazole (MIC50 0.125/0.25 mg/L). With the exception of amphotericin B, low essential agreement between gradient test and microdilution was recorded for all antifungals in both species (0-68%). Both species show distinct morphology traits on ChromAgar Orientation and Columbia blood agar, which can be used for differentiation if no MALDI-TOF or molecular identification is available.
Conclusion: Most bloodstream infections in Germany were caused by M. clavatus. Voriconazole and posaconazole were the most active antifungals. Gradients tests show unacceptably low agreement and should preferably not be used for susceptibility testing of Magnusiomyces spp.