Abstract
Aspergillus species such as A. fumigatus and A. flavus are now the major cause of aspergillosis, which leads to a high mortality in immunocompromised hosts, especially in hematology patients. For the treatment of invasive aspergillosis (IA), amphotericin B and itraconazole have been the drugs of choice although amphotericin B therapy is limited by toxicity. Itraconazole is a triazole antifungal drug with good in vitro activity against Aspergillus spp. and has less toxicity. These two antifungal agents have been widely used to treat IA in China during the last decade. However, the extensive use of these compounds has been associated with the resistance. The earliest such findings were amongst Candida species. Recently, A. fumigatus isolates with in vitro resistance to itraconazole have been described. Also, an A. flavus isolate was found to be resistant to amphotericin B in vitro.
We report the acquired itraconazole resistance in an A. fumigatus isolated from an aspergilloma patient treated with itraconazole in 2005: six A. fumigatus isolates were recovered at different times from the patient's sputum. After careful evaluation for antifungal susceptibility in vitro, the serial isolates were typed by RAPD with five different primers to confirm the identity. The interesting finding was that the itraconazole MIC against the pre-treatment isolate was 0.25 mg/L, while the second isolate, recovered after 6 months of itraconazole therapy, had an itraconazole MIC of >16 mg/L. The third strain was isolated two months after the therapy was discontinued and the itraconazole MIC was 0.5 mg/L. The MIC against the last three isolates acquired from the restoration of itraconazole therapy of 4 to 7 month was >16 mg/L.
The molecular mechanisms of Aspergillus species resistance to these antifungals was studied through mutation detection of the target gene of the azoles ERG11 and the expression changes of pump genes such as MDR3. Cross resistance among the antifungal agents was detected and the role of ERG3 was studied. Our study revealed that the acquired itraconazole resistance of A. fumigatus may result from mutations in ERG11 gene.
