gms | German Medical Science

Aspergillosis due to Aspergillus fumigatus (A. fum.) is a common and life-threatening infection in immunocompromised patients. A. fum. is increasingly reported to be resistant to azoles essentially in prophylaxis and/or therapy of aspergillosis. Resistance is often associated with alterations in cyp51A coding the 14α-demethylase which is inhibited by azoles [1], [2], [3], [4].

Here we present 25 isolates from 20 patients, suspected for resistance to azoles having been examined at the Robert Koch-Institut (Berlin) between 2010 and 2013. Most of the isolates (n=20) were from the respiratory tract of patients with cystic fibrosis (CF, n=15), 4 isolates were from non-CF patients and 1 isolate from one patient with no clinical data reported. Antifungal susceptibility testing of the isolates to itraconazole (ICZ), posaconazole and voriconazole was performed according to CLSI-guidelines. Analysis of cyp51A was done by sequencing and alignment with GenBank sequences.

9 isolates proved to be highly resistant to ICZ (MIC >8 mg/L) showing different susceptibility patterns for the other azoles. In 7 (78 %) of these isolates a mutation in cyp51A could be detected. The most common amino acid substitution L98H (67 %) resulted in an in vitro resistance to all azoles. No mutation could be detected in two isolates highly resistant to ICZ. In 15/16 azole susceptible isolates no mutations were found, but 5 single nucleotide polymorphisms (SNPs) were detected in one azole susceptible isolate. To our knowledge, it is the first time this 5-fold SNP combination is described in a clinical isolate in Germany.

In conclusion, in vitro azole resistance of A. fum. was detectable in most isolates by sequencing cyp51A. Mutations in this gene do not result necessarily in an in vitro resistance. For a better understanding of such mutations a knowledge of the spatial conformation of cyp51A is needed. Finally, azole resistance mechanisms which are not related to alterations in the target enzyme remain to be elucidated.