Frequency and evolution of Azole resistance in Aspergillus fumigatus associated with treatment failure

Abstract

Azoles are the mainstay of oral therapy for aspergillosis. Azole resistance in Aspergillus has been reported infrequently. The first resistant isolate was detected in 1999 in Manchester, UK. In a clinical collection of 519 A. fumigatus isolates, the frequency of itraconazole resistance was 5%, a significant increase since 2004 (p<0.001). Of the 34 itraconazole-resistant isolates we studied, 65% (22) were cross-resistant to voriconazole and 74% (25) were cross-resistant to posaconazole. Thirteen of 14 evaluable patients in our study had prior azole exposure; 8 infections failed therapy (progressed), and 5 failed to improve (remained stable). Eighteen amino acid alterations were found in the target enzyme, Cyp51A, 4 of which were novel. A population genetic analysis of microsatellites showed the existence of resistant mutants that evolved from originally susceptible strains, different cyp51A mutations in the same strain, and microalterations in microsatellite repeat number. Azole resistance in A. fumigatus is an emerging problem and may develop during azole therapy.

Figure 1

Azole resistance in clinical Aspergillus fumigatus isolates received in the Regional Mycology Laboratory Manchester, UK, 1997–2007. Overall azole resistance for each year is shown above each column as a percentage. Data do not include sequential isolates from the same patient.

Figure 2

Unrooted phylogenetic tree showing the genetic relationship of isolates from 7 patients.The genetic relationship of these isolates is shown in relation to each other and to 18 other isolates. AF numbers belong to a collection of >200 isolates, held in Manchester, UK. ATCC, American Type Culture Collection; CBS, Centraalbureau voor Schimmelcultures; FGSC, Fungal Genetics Stock Center. Bootstrap values >90 only are shown. Scale bar indicates nucleotide substitutions per site.