Using Myconostica's real-time PCR assay for Aspergillus spp., MycAssay™ Aspergillus , researchers in Manchester, UK and Newark, USA, have directly detected azole resistance in people with aspergillosis, without first culturing the fungus Aspergillus on agar1.
The methods are similar to those used for HIV, MRSA and influenza, but have never been applied to fungal infections previously.
Antifungal triazole resistance rates are rising internationally, possibly related to fungicide use in agriculture and long treatment courses in patients. The triazoles itraconazole (Johnson & Johnson), voriconazole (Pfizer) and posaconazole (Merck) have annual sales of over $1bn annually. Conventional diagnosis of aspergillosis is limited by poor culture yield, and so the frequency of triazole resistance is unclear. In this work published in the prestigious US journal Clinical Infectious Diseases, the presence of Aspergillus was detected using MycAssay™ Aspergillus in many more samples than in agar culture, and 55% were found to contain triazole resistance markers. This is an extraordinarily high rate of resistance. The authors conclude that; 'These findings have major implications for the sustainability of triazoles for human antifungal therapy'.
The study involved analyzing phlegm from patients with allergic and chronic lung disease caused by Aspergillus; 45 of 61 (74%) were positive by MycAssay™ Aspergillus test, compared with 11% by agar culture. While 55% had a resistance marker present remarkably 6 of 8 (75%) people who had never been treated with an azole had a resistance marker. Among 230 strains cultured in the clinical lab in 2008 and 2009 in Manchester 64 (28%) were azole resistant2.
1 Denning DW, Park S, Lass-Florl C, Fraczek MG, Kirwan M, Gore R, Smith J, Bueid A, Bowyer P, Perlin DS. High frequency triazole resistance found in non-culturable Aspergillus fumigatus from lungs of patients with chronic fungal disease. Clin Infect Dis In press.
2 Bueid A, Howard SJ, Moore CB, Richardson MD, Harrison E, Bowyer P, Denning DW. Azole antifungal resistance in Aspergillus fumigatus - 2008 and 2009. J Antimicrob Chemother 2010;65:2116-8.