Reply to “Are the TR₄₆/Y121F/T289A Mutations in Azole-Resistant Aspergillosis Patient Acquired or Environmental?”

REPLY

We welcome the comments by Buil et al. (1). Over the past 5 years, concern has been increasing regarding azole-resistant Aspergillus fumigatus isolates. Azole-resistant A. fumigatus isolates have been primarily described throughout Europe, India, China, and Australia (2). Only recently have there been several azole-resistant isolates described in the United States (3). In contrast to other countries, there have been no environmental azole-resistant Aspergillus isolates described in the United States.

Buil et al. state that the statement “emergence of resistance in AF50593 occurred during voriconazole therapy” is speculative since there was no genotyping performed on these isolates. We absolutely agree with Buil et al.: in fact, although not reported in this study, we also recovered four additional isolates of A. fumigatus between isolate 1 (AF47381) and the final isolate (AF50593) (4). In fact, all of the Aspergillus isolates recovered between the first and final isolates had identical susceptibility profiles and were all susceptible to voriconazole. Although we did not perform genotyping on any of the isolates, we felt relatively sure that the final azole-resistant isolate derived from the initially recovered isolate or strain. However, there have been several smaller epidemiological studies describing the recovery of several different strains of Aspergillus in a single patient (5). It is certainly theoretically possible in this case.

However, the primary aim of this case study was to report the first actual case of azole-resistant A. fumigatus in the United States, thus, bringing to the forefront the fact that we now have azole-resistant Aspergillus spp in the United States, and we should consider this when a patient fails antifungal therapy. In fact, this would be the 2nd clinical isolate reported to have azole resistance in the United States. The initial isolate was characterized and reported by Wiederhold et al., describing two different isolates from the University of Texas Health Science Center at San Antonio (UTHSCSA) collection dating back to 2007 and having the same Cyp51 mutation as our isolate (3). Second, we also wanted to show that the Cyp51 mutations revealed in this azole-resistant isolate are similar to the mutations described in the environmental Aspergillus isolates that have been described in other parts of the world. In fact, the same mutations were described by Wiederhold et al. in one isolate dating back to 2008 (Arizona) and in a clinical reference isolate. Furthermore, since azole-resistant isolates have not been described in the United States until recently, we felt relatively sure that the final azole-resistant isolate was not acquired from the environment but was developed while the patient was on voriconazole therapy. In fact, when taken all together, this patient could be considered the “perfect storm” for generating a resistant fungal isolate for a variety of reasons, as stated by Buil et al. (1). First, he was severely immunosuppressed for many months after the lung transplant. Second, he was on long-term azole therapy with chronic lung disease and had a continuous Aspergillus empyema infection (i.e., Aspergillus in a cavity where asexual reproduction may occur) that was never completely cured, which theoretically enhances the probability of selection. Finally, we were able to recover five pan-susceptible isolates of A. fumigatus, and only the final one showed voriconazole resistance.

In conclusion, we agree with Buil et al. that improved awareness of azole resistance is necessary and that clinical and environmental surveys searching for azole resistance and mechanisms of resistance are warranted to better identify high-risk populations and possible environmental sources of azole resistance.