Rapid Antifungal Susceptibility Determination for Yeast Isolates by Use of Etest Performed Directly on Blood Samples from Patients with Fungemia

Abstract

We prospectively determined the antifungal susceptibility of yeast isolates causing fungemia using the Etest on direct blood samples (195 prospectively collected and 133 laboratory prepared). We compared the Etest direct (24 h of incubation) with CLSI M27-A3 and the standard Etest methodologies for fluconazole, voriconazole, posaconazole, isavuconazole, caspofungin, and amphotericin B. Strains were classified as susceptible, resistant, or nonsusceptible using CLSI breakpoints (voriconazole breakpoints were used for posaconazole and isavuconazole). Categorical errors between Etest direct and CLSI M27-A3 for azoles were mostly minor. No errors were detected for caspofungin, and high percentages of major errors were detected for amphotericin B. For the azoles, false susceptibility (very major errors) was found in only two (0.6%) isolates (Candida tropicalis and C. glabrata). False resistance (major errors) was detected in 46 (14%) isolates for the three azoles (in 23 [7%] after excluding posaconazole). Etest direct of posaconazole yielded a higher number of major errors than the remaining azoles, especially for C. glabrata, Candida spp., and other yeasts. Excluding C. glabrata, Candida spp., and other yeasts, the remaining species did not yield major errors. Etest direct for fluconazole, voriconazole, isavuconazole, and caspofungin shows potential as an alternative to the CLSI M27-A3 procedure for performing rapid antifungal susceptibility tests on yeast isolates from patients with fungemia. Etest direct is a useful tool to screen for the presence of azole-resistant and caspofunginnonsusceptible strains.

Agreement of Direct Antifungal Susceptibility Testing from Positive Blood Culture Bottles with the Conventional Method for Candida Species

“…This approach has reduced the time from positivity of blood culture to preliminary reporting of susceptibility results. This practice has also been evaluated for yeasts using Etest, which showed a 98% agreement rate between direct susceptibility testing and the conventional method (13,14). A few other studies have evaluated direct susceptibility testing using Vitek antifungal cards, Sensititre YeastOne, and flow cytometry and have had various results (15)(16)(17).…”

Candida parapsilosis complex water isolates from a haemodialysis unit: biofilm production and in vitro evaluation of the use of clinical antifungals

“…Dispersed cells of Candida are responsible for candidemia and invasive disseminated candidiasis, which are among the most serious forms of infection and lead to the highest mortality rates (Colombo et al 2006, Bruder-Nascimento et al 2010. Isolates with MBIC n-folds higher than the MIC n (%) a: MIC amphotericin B = 2 µg/mL (Clinical and Laboratory Standards Institute M27-A3 document) (Guinea et al 2010). …”

“…Minimal inhibitory concentration (MIC) values for azoles were determined visually, after 24 h of incubation, as the lowest concentration of drug that caused a significant diminution (≥ 50% inhibition) of growth below control levels and the MIC of AMB was determined as the lowest concentration that prevented any discernible growth. Strains with MICs of > 1 μg/mL for AMB were considered resistant (CLSI 2008, Diekema et al 2009, Guinea et al 2010. Quality control strains C. parapsilosis ATCC 22019, Candida krusei ATCC 6258 were included in each test.…”

Pattern of susceptibility to azoles by E test method in candidemia patients

“…For azoles, significant inhibition, 80% decrease in growth density is required to visually select the end point. 8 Interpretation was done as per CLSI M27-A3 document guidelines. MIC50 and MIC90 (the MIC at which 50% and 90% of the isolates are inhibited) were also calculated.…”