Antifungal activity and killing kinetics of anidulafungin, caspofungin and amphotericin B against Candida auris.

BACKGROUND

Candida auris is an emerging MDR pathogen. It shows reduced susceptibility to azole drugs and, in some strains, high amphotericin B MICs have been described. For these reasons, echinocandins were proposed as first-line treatment for C. auris infections. However, information on how echinocandins and amphotericin B act against this species is lacking.

OBJECTIVES

Our aim was to establish the killing kinetics of anidulafungin, caspofungin and amphotericin B against C. auris by time-kill methodology and to determine if these antifungals behave as fungicidal or fungistatic agents against this species.

METHODS

The susceptibility of 50 C. auris strains was studied. Nine strains were selected (based on echinocandin MICs) to be further studied. Minimal fungicidal concentrations, in vitro dose-response and time-kill patterns were determined.

RESULTS

Echinocandins showed lower MIC values than amphotericin B (geometric mean of 0.12 and 0.94 mg/L, respectively). Anidulafungin and caspofungin showed no fungicidal activity at any concentration (maximum log decreases in cfu/mL between 1.34 and 2.22). On the other hand, amphotericin B showed fungicidal activity, but at high concentrations (≥2.00 mg/L). In addition, the tested polyene was faster than echinocandins at killing 50% of the initial inoculum (0.92 versus >8.00 h, respectively).

CONCLUSIONS

Amphotericin B was the only agent regarded as fungicidal against C. auris. Moreover, C. auris should be considered tolerant to caspofungin and anidulafungin considering that their MFC:MIC ratios were mostly ≥32 and that after 6 h of incubation the starting inoculum was not reduced in >90%.