Emergence of resistant in Germany.

Background: is the second leading fungal pathogen causing candidaemia and invasive candidiasis in Europe. This yeast is recognized for its rapid ability to acquire antifungal drug resistance.

Objectives: We systematically evaluated 176 isolates submitted to the German National Reference Center for Invasive Fungal Infections (NRZMyk) between 2015 and 2019 with regard to echinocandin and fluconazole susceptibility.

Methods: Susceptibility testing was performed using a reference protocol (EUCAST) and a range of commercial assays. Hot spot regions of the echinocandin target genes were sequenced using Sanger sequencing.

Results: In total, 84 of 176 isolates were initially classified as anidulafungin-resistant based on EUCAST testing. Of those, 71 harboured mutations in the glucan synthase encoding genes (13% in , 87% in 2). Significant differences in anidulafungin MICs were found between distinct mutation sites. 11 wild-type (WT) isolates initially classified as resistant exhibited anidulafungin MICs fluctuating around the interpretation breakpoint upon re-testing with multiple assays. Two WT isolates consistently showed high anidulafungin MICs and thus must be considered resistant despite the absence of target gene mutations. Over one-third of echinocandin-resistant strains displayed concomitant fluconazole resistance. Of those, isolates linked to bloodstream infection carrying a change at Ser-663 were associated with adverse clinical outcome.

Conclusions: Resistant strains are emerging in Germany. Phenotypic echinocandin testing can result in misclassification of susceptible strains. genotyping aids in detecting these strains, however, echinocandin resistance may occur despite a wild-type genotype.