Emergence of Azole Resistance in Aspergillus fumigatus and Spread of a Single Resistance Mechanism.

Abstract

A B S T R A C T BackgroundResistance to triazoles was recently reported in Aspergillus fumigatus isolates cultured from patients with invasive aspergillosis. The prevalence of azole resistance in A. fumigatus is unknown. We investigated the prevalence and spread of azole resistance using our culture collection that contained A. fumigatus isolates collected between 1994 and 2007. Methods and FindingsWe investigated the prevalence of itraconazole (ITZ) resistance in 1,912 clinical A. fumigatus isolates collected from 1,219 patients in our University Medical Centre over a 14-y period. The spread of resistance was investigated by analyzing 147 A. fumigatus isolates from 101 patients, from 28 other medical centres in The Netherlands and 317 isolates from six other countries. The isolates were characterized using phenotypic and molecular methods. The electronic patient files were used to determine the underlying conditions of the patients and the presence of invasive aspergillosis. ITZ-resistant isolates were found in 32 of 1,219 patients. All cases were observed after 1999 with an annual prevalence of 1.7% to 6%. The ITZ-resistant isolates also showed elevated minimum inhibitory concentrations of voriconazole, ravuconazole, and posaconazole. A substitution of leucine 98 for histidine in the cyp51A gene, together with two copies of a 34-bp sequence in tandem in the gene promoter (TR/L98H), was found to be the dominant resistance mechanism. Microsatellite analysis indicated that the ITZ-resistant isolates were genetically distinct but clustered. The ITZ-sensitive isolates were not more likely to be responsible for invasive aspergillosis than the ITZ-resistant isolates. ITZ resistance was found in isolates from 13 patients (12.8%) from nine other medical centres in The Netherlands, of which 69% harboured the TR/L98H substitution, and in six isolates originating from four other countries. ConclusionsAzole resistance has emerged in A. fumigatus and might be more prevalent than currently acknowledged. The presence of a dominant resistance mechanism in clinical isolates suggests that isolates with this mechanism are spreading in our environment.

Molecular typing and in-vitro activity of azoles against clinical isolates of Aspergillus fumigatus and A. niger in Japan

“…Mutation hotspots confirmed to cause resistance have been characterized in the gene at codons 54, 98, and 220 [10,11]. Therefore, we also sequenced cyp51A of strain 5402, in accordance with a previous report [8], and detected a novel mutation (F332K) in the gene (DDBJ accession no.…”

“…In this study, we identified one isolate (4.3%) of ITZ-resistant A. fumigatus. In the future, ITZ resistant A. fumigatus may increase in Japan and may be an emerging problem [9,11].…”

Multi-Resistant Aspergillosis due to Cryptic Species

“…Acquired (or secondary) resistance, in response to drug exposure, has been described extensively in A. fumigatus and now has worldwide distribution and has been shown to be increasing in some regions [3][4][5]. Cryptic species may also potentially acquire resistance.…”

Novel mutations in CYP51B from Penicillium digitatum involved in prochloraz resistance

“…In Aspergillus fumigatus, the F495I substitution of CYP51 (corresponding to F506I in PdCYP51B) was recently reported to be involved in the resistance to azole antifungals. However, this substitution does not occur alone but arises with the TR/L98H or S297T mutation (Mellado et al, 2007;Snelders et al, 2008;Lockhart et al, 2011). Therefore, we hypothesize that the MR phenotype of strains depends on the simultaneous substitutions of G459S and F506I, which change the conformation of the heme environment and/or block the entry of prochloraz into the heme pocket via steric hindrance.…”