Prevalence and molecular characterization of azole resistance in Aspergillus spp. isolates from German cystic fibrosis patients.

OBJECTIVES: Aspergillus spp. are the most frequently isolated filamentous fungi in the sputum of patients with cystic fibrosis (CF). Resistance to the azoles, the mainstay of current antifungal therapy, has been increasingly observed worldwide, but few data are available on the resistance of Aspergillus spp. in German CF patients. This study investigated the epidemiology of Aspergillus spp. and the molecular origin of azole resistance in a large German CF centre.

METHODS: In total, 2677 respiratory samples from 221 CF patients collected between April 2010 and April 2013 were analysed; of these, 573 yielded Aspergillus spp., which were screened for azole resistance. Isolates with reduced susceptibility to itraconazole and/or voriconazole were tested according to the EUCAST reference procedure. Sequencing of cyp51A, the target of azole antifungals, was performed in all resistant isolates.

RESULTS: Six isolates obtained from four patients were highly resistant to itraconazole (all identified as Aspergillus fumigatus sensu stricto); five of them were pan-azole resistant. The TR34/L98H mutation was the most frequent mutation identified in azole-resistant isolates (n = 4), followed by M220L and TR46/Y121F/T289A, a mutation previously reported from Belgium and the Netherlands only. Three of four patients harbouring azole-resistant A. fumigatus had not received any prior azole treatment.

CONCLUSIONS: Resistance to azoles in Aspergillus spp. is still infrequent in German CF patients and is mainly caused by the TR34/L98H mutation. Worryingly, pan-azole-resistant TR46/Y121F/T289A has spread to Germany. Azole resistance has to be considered also in azole-naive CF patients and susceptibility testing of Aspergillus spp. isolates should be performed in all patients requiring treatment.