Resistance to echinocandins in Candida can be detected by performing the Etest directly on blood culture samples [PublishAheadOfPrint]

Background: We examined the rapid evaluation of susceptibility to echinocandins in Candida spp. using the Etest performed directly on positive blood cultures and anidulafungin-containing agar plates.

Methods: We prospectively collected 80 positive blood cultures (Bactec™-FX system, Becton-Dickinson, Cockeysville, Maryland, USA) with echinocandin-susceptible Candida spp (n=60) and echinocandin-intermediate C. parapsilosis (n=20) from patients with candidemia. Additionally, blood culture bottles of nonfungemic/bacteremic patients were spiked with 35 echinocandin-resistant Candida spp. isolates. A total of 2-4 drops of medium from each bottle was stroked directly both onto RPMI 1640 agar plates with micafungin and anidulafungin Etest strips (ET_DIR) and on Sabouraud agar plates containing 2 mg/L of anidulafungin. Isolates were tested according to the EUCAST method and Etest standard (ET_SD). Essential and categorical agreement between methods was calculated.

Results: Essential agreement and categorical agreement between EUCAST and ET_DIR and ET_SD were both >97.4%. The essential agreement between ET_DIR and EUCAST for both echinocandins was >97%. The categorical agreement between the FKS sequence (gold standard) and ET_DIR was 97.4%. The ET_DIR MIC of anidulafungin and micafungin (≥ 0.19 mg/L and ≥ 0.064 mg/L, respectively) effectively separated all susceptible/FKS wild-type isolates from the resistant/FKS mutant isolates. The categorical agreement (62.6%) between EUCAST and growth on anidulafungin-containing plates was poor, with the best agreement observed for C. glabrata (94.2%).

Conclusions: When performed directly on positive blood cultures from patients with candidemia, the Etest with micafungin and anidulafungin is a reliable procedure for a rapid testing of susceptibility to echinocandins in Candida spp. isolates.

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