Multicenter Evaluation of the New Vitek 2 Yeast Susceptibility Test Using New CLSI Clinical Breakpoints for Fluconazole

Abstract

A fully automated antifungal susceptibility test system recently updated to reflect the new species-specific clinical breakpoints (CBPs) of fluconazole for Candida (Vitek 2 AF03 yeast susceptibility test; bioMérieux, Inc., Durham, NC) was compared in three different laboratories with the Clinical and Laboratory Standards Institute (CLSI) reference broth microdilution (BMD) method by testing 2 quality control strains, 10 reproducibility strains (4 Candida species and 6 Cryptococcus neoformans strains), and 746 isolates of Candida species (702 isolates, 13 species) and 44 isolates of C. neoformans against fluconazole. Excellent essential agreement (EA) (within 2 dilutions) between the reference and Vitek 2 MICs was observed for fluconazole and Candida species (94.0%). The EA was lower for fluconazole and C. neoformans at 86.4%. The mean times to a result with the Vitek 2 test were 9.1 h for Candida species and 12.1 h for C. neoformans. Categorical agreement (CA) between the two methods was assessed by using the new species-specific CBPs. For less common species without fluconazole CBPs, the epidemiological cutoff values (ECVs) were used to differentiate wild-type (WT; MIC, <ECV) from non-WT (MIC, >ECV) strains. The CAs between the two methods were 92.0% for Candida species (0.3% very major errors [VME] and 2.6% major errors [ME]) and 84.1% for C. neoformans (4.5% VME and 11.4% ME). The updated Vitek 2 AF03 IUO yeast susceptibility system is comparable to the CLSI BMD reference method for testing the susceptibility of clinically important yeasts to fluconazole when using the new (lower) CBPs and ECVs.T he automation of laboratory testing has clear advantages in test standardization, reproducibility and timeliness of results, and savings in labor and reagents (1, 2). Whereas total laboratory automation has been slow to arrive in clinical microbiology laboratories, automated microbial identification and antimicrobial susceptibility testing systems are widely used in microbiology laboratories (1, 2). These systems have been broadly applied in the testing of bacteria but, aside from the identification of yeasts, have not been useful for fungi (2).Antifungal susceptibility testing of Candida species and Cryptococcus neoformans has been standardized by the Clinical and Laboratory Standards Institute (CLSI) Subcommittee on Antifungal Susceptibility Testing (3), and until recently, the only commercially available methods for performing such testing have been manual methods such as the Sensititre Yeast One (TREK Diagnostic Systems, Cleveland, OH) and the Etest (bioMérieux, Inc., Durham, NC). The recent introduction of the Vitek 2 yeast susceptibility test (bioMérieux, Inc.) has provided a completely automated means of performing antifungal susceptibility testing of yeasts that has been shown to produce reproducible, rapid, and accurate results consistent with those obtained with the CLSI reference broth microdilution (BMD) method for amphotericin B, flucytosine, fluconazole, and voriconazole (4-9). The ease of performing an...

Susceptibility Test for Fungi: Clinical and Laboratorial Correlations in Medical Mycology

“…However, Vitek 2(r) results are reproducible, accurate, present a strong correlation with those obtained with the CLSI and the AFST-EUCAST reference methods for fluconazole, amphotericin B, flucytosine, and voriconazole. The correlation with the reference methods was also very good when resistance to antifungals was studied 43 , 47 , 51 .…”

Invasive Fungal Infections and Approaches to Their Diagnosis

“…This automated approach allows for the standardisation of all the critical parameters known for antifungal susceptibility testing: inoculum preparation, filling of the device, duration and temperature of incubation, and MIC endpoint determination. A multicentre evaluation of the VITEK 2 Yeast Susceptibility Test for fluconazole demonstrated a high level of reproducibility (100%), an essential agreement (MIC AE1-log 2 dilution) of 93.7-97.9%, and a categorical agreement of 88.3-97.2% when compared to the reference BMD results ,2007bPfaller, Diekema, Procop, & Wiederhold, 2014;. Notably, the VITEK 2 fluconazole MIC results were available after only 10-26 h of incubation (mean, 13 h).…”

“…Nevertheless, C. albicans remains the most common fungal pathogen Pfaller & Diekema, 2007;Pfaller, Chaturvedi, et al, 2012;Pfaller, Neofytos, et al, 2012;Pfaller, Woosley, Messer, Jones, & Castanheira, 2012;Pfaller, Diekema, Procop, & Wiederhold, 2014; and A. fumigatus is the commonest mould pathogen Morgan et al, 2005;Pfaller, Pappas, & Wingard, 2006). Likewise, Candida spp., Aspergillus spp., and C. neoformans account for more than 80% of all fungal infections in blood and marrow transplant (BMT), solid-organ transplant, and other immunocompromised patient populations Bow, 2005;Marcos & Pincus, 2013;Marr, 2005;Marty et al, 2005; (Table 3).…”

Clinical perspectives on echinocandin resistance among Candida species

“…The overall clinical impact of caspofungin MIC variability is somewhat mitigated by the fact that an overwhelming majority of hospitals do not use reference broth microdilution methods, but rather commercialized assays such as Sensititre YeastOne (SYO, Trek Diagnostics, Cleveland, United States) and Etest (Biomerieux, Marcy-I'Etoile, France), or automated systems like Vitek 2 (Biomerieux) [45,46]. Echinocandin MICs generated by these methods and reference methods demonstrate good essential agreement (MICs within a two-fold dilution), but categorical agreement (defining isolates as susceptible, intermediate or resistant) using reference breakpoints may be lower [47,48].…”