Comparison of Three Statistical Methods for Establishing Tentative Wild-Type Population and Epidemiological Cutoff Values for Echinocandins, Amphotericin B, Flucytosine, and Six Candida Species as Determined by the Colorimetric Sensititre YeastOne Method

Abstract

The Sensititre YeastOne (SYO) method is a widely used method to determine the susceptibility of Candida spp. to antifungal agents. CLSI clinical breakpoints (CBP) have been reported for antifungals, but not using this method. In the absence of CBP, epidemiological cutoff values (ECVs) are useful to separate wild-type (WT) isolates (those without mechanisms of resistance) from non-WT isolates (those that can harbor some resistance mechanisms), which is the goal of any susceptibility test. The ECVs for five agents, obtained using the MIC distributions determined by the SYO test, were calculated and contrasted with those for three statistical methods and the MIC 50

Antifungal Susceptibilities of Candida Isolates Causing Bloodstream Infections at a Medical Center in Taiwan, 2009-2010

“…The MIC ranges of voriconazole and posaconazole among C. tropicalis isolates (n ϭ 98) were 0.03 to Ͼ8 g/ml (MIC 90 , 0.25 g/ml) and 0.06 to Ͼ8 g/ml (MIC 90 , 0.5 g/ml). These findings contrast greatly with previous reports (12,15). The MIC 90 s of voriconazole and posaconazole in the present study were 4-fold higher than those reported by Pfaller et al, who demonstrated that the MICs of voriconazole and posaconazole among C. tropicalis isolates (n ϭ 1,895) ranged from 0.007 g/ml to 4 g/ml (MIC 90 , 0.06 g/ml) and from 0.007 g/ml to 2 g/ml (MIC 90 , 0.12 g/ml), respectively (14).…”

“…Although the agreement of the SYO method and reference CLSI method with 24-h MICs was reported to be 95% to 99% for all Candida species and antifungal agents (8)(9)(10), these methods may fail to give identical results on certain occasions (8,9). The epidemiological cutoff values determined by the 24-h SYO method differ by within one dilution from those determined by the 24-h CLSI BMD method (12). This might limit the use of CLSI breakpoints for interpretation of the results obtained by the SYO method.…”

“…Important recent advances in antifungal susceptibility testing include validation of 24-h reading times for all antifungal agents and the establishment of species-specific clinical breakpoints (CBPs) and epidemiological cutoff values (ECVs) for several commonly used antifungal agents (8,(13)(14)(15)(16)(17)(18)(19). The currently proposed species-specific ECVs for several antifungal agents determined by the 24-h CLSI broth microdilution (BMD) method and the 24-h SYO system are useful for detecting the emergence of resistance among Candida isolates (8,9,12). The revised CBPs for interpreting susceptibility to azoles (fluconazole and voriconazole) and echinocandin among Candida isolates not only predict clinical outcome but also provide a more sensitive means of identifying strains with acquired or mutational resistance mechanisms (8,13,14,20).…”

“…Antifungal susceptibility testing of Candida species has been standardized and refined to the species-specific level and now plays a useful role in managing Candida infections (8). Furthermore, several commercial antifungal susceptibility testing methods, including the Etest (AB Biodisk, Solna, Sweden), Vitek 2 (bioMérieux Vitek, St. Louis, MO, USA), and the Sensititre YeastOne (SYO) system (Trek Diagnostic Systems, Ltd., East Grinstead, United Kingdom), have also been evaluated for their performance among Candida isolates and compared with the standard method recommended by the Clinical and Laboratory Standards Institute (CLSI) (9)(10)(11)(12). Important recent advances in antifungal susceptibility testing include validation of 24-h reading times for all antifungal agents and the establishment of species-specific clinical breakpoints (CBPs) and epidemiological cutoff values (ECVs) for several commonly used antifungal agents (8,(13)(14)(15)(16)(17)(18)(19).…”

Antifungal Susceptibility Profiles of Bloodstream Yeast Isolates by Sensititre YeastOne over Nine Years at a Large Italian Teaching Hospital

“…The remaining 17 isolates belonged to those Candida species (e.g., C. kefyr, C. pelliculosa) for which amphotericin B or flucytosine ECVs were not defined (29). Tentative ECVs for the SYO method were recently proposed, and the median values obtained by the five approaches employed for flucytosine and C. albicans, C. parapsilosis, and C. tropicalis were almost identical to those obtained with the CLSI method (41). For these species, the MIC ranges of flucytosine obtained in the present study were similar to those obtained in two earlier surveys, both of which used the SYO method (20,40), but a higher proportion of our C. parapsilosis complex or C. tropicalis isolates exhibited flucytosine MICs greater than the CLSI ECVs.…”