Comparative Evaluation of Sensititre YeastOne and CLSI M38-A2 Reference Method for Antifungal Susceptibility Testing of Aspergillus spp. against Echinocandins

Abstract

Sensititre YeastOne (YO) panels were assessed for in vitro susceptibility testing of echinocandins against 39 isolates of Aspergillus fumigatus, A. flavus, and A. terreus, including two echinocandin-resistant A. fumigatus strains, using different inocula (10 3 , 10 4 , and 10 5 CFU/ml), incubation times (16 to 48 h), and endpoints (first blue or purple well) and compared to CLSI M38-A2. The best agreement was found with an inoculum of 10 4 CFU/ml, incubation times of 20 h for A. flavus and of 30 h for A. fumigatus and A. terreus, and reading the first purple well. The reproducibility within Ϯ1 2-fold dilutions was 100% for all three echinocandins. YO color endpoints were 2 to 3 2-fold dilutions lower than CLSI minimum effective concentrations (MECs) of caspofungin and 1 to 2 2-fold dilutions higher than CLSI MECs of micafungin. For anidulafungin, off-scale YO color endpoints were observed. Nevertheless, A. fumigatus echinocandin-resistant isolates were detected after 24 h of incubation.KEYWORDS echinocandins, Aspergillus spp., Sensititre, antifungal susceptibility testing, MEC A spergillus isolates with reduced susceptibility to current antifungal agents have been increasingly reported, highlighting the importance of antifungal susceptibility testing in clinical microbiology laboratory routine (1). In vitro reduced susceptibility of Aspergillus fumigatus isolates to echinocandins can be developed via FKS-dependent and FKS-independent mechanisms (2). Although clinical resistance of Aspergillus to echinocandins is limited (3), breakthrough infections in patients treated with echinocandins has been reported (4), and non-wild-type clinical isolates with minimal effective concentrations (MECs) above the epidemiological cutoff value have been found (5). Sensititre YeastOne (YO) is an adapted susceptibility system of the microbroth CLSI method based on the M27-A3 standard for yeasts, which uses alamarBlue as a colorimetric indicator. Sensititre YeastOne has been extensively evaluated for yeasts. There are fewer studies for molds, demonstrating high levels of agreement with the reference methodology for amphotericin B and azoles with Aspergillus spp. (6-12), while limited data exist for echinocandins. Since Sensititre YeastOne is widely used in routine microbiology laboratories, the aim of the present study was to assess its performance for in vitro susceptibility testing of echinocandins against the three most commonly isolated Aspergillus spp. -A. fumigatus, A. flavus, and A. terreus-compared

Comparative Evaluation of Micronaut-AM and CLSI broth micro-dilution method for antifungal susceptibility testing of Aspergillus species against four commonly used antifungals

“…and low echinocandin concordance by Siopi et al15 12 out 56 A fumigatus isolates tested by Dunne et al had amphotericin MIC of 2mg/L. Interestingly, we obtained similar results when locally validating YO and a significant number of isolates in our collection were from cystic fibrosis patients (data not published).…”

In vitro susceptibility of dematiaceous fungi to nine antifungal agents determined by two different methods

“…Under such circumstances, the value of MEC was lower than that of the MIC evaluated by colour shift. The low agreements between the two methods were also reported in Aspergillus when against echinocandins …”

“…This method has the advantages of shortening the test time, simplifying the procedure and facilitating the determination of endpoints . The YeastOne® method has already been applied in Candida , Aspergillus and Dermatophytes, but little is known about its application to black fungi …”

“…14,16,25 The YeastOne® method has already been applied in Candida, Aspergillus and Dermatophytes, but little is known about its application to black fungi. 16,[28][29][30][31][32] In the current study, nine antifungal agents were selected for the test. Azoles are highly used in the treatment and the prevention of mycoses due to their broad spectrum activity, 33 and as such are a generally wise choice until more precise data are available.…”

“…The low agreements between the two methods were also reported in Aspergillus when against echinocandins. 29 This study was the first research on the comparison between the Sensititre YeastOne® method and the CLSI reference method for testing the in vitro susceptibility of a broad spectrum of dematiaceous fungi. Triazoles other than fluconazole were the most powerful drugs against black fungi in vitro.…”