To investigate the in vitro activity of nitroxoline against a molecularly characterized collection of clinical Candida auris isolates.
Thirty-five clinical isolates of C. auris from diverse sources representing all five different C. auris clades were included in the study. Nitroxoline activity was assessed using broth microdilution. Additionally, susceptibility testing by disk diffusion was assessed on RPMI1640 and Mueller Hinton agar plates. Minimal inhibitory concentrations of the antifungals fluconazole, voriconazole, amphotericin B and anidulafungin were determined.
Nitroxoline MICs ranged from 0.125-1 mg/L (MIC 0.25/0.5 mg/L). Compared to amphotericin B (>1 mg/L in 4/35 isolates), anidulafungin (>0.06 mg/L in 26/35 isolates) and fluconazole (MIC >4 mg/L in 31/35 isolates) in vitro activity of nitroxoline was high. Isolates belonging to clade I had marginally lower nitroxoline MICs (range 0.125-0.5 mg/L, mean MIC 0.375 mg/L) compared to clade III (range 0.5 – 1 mg/L, mean MIC 0.7), p=0.094. The correlation of MIC and inhibition zones by disk diffusion was good when using RPMI-agar for disk diffusion, with a Pearson’s correlation coefficient of -0.74 (95% confidence interval -0.86 to -0.54).
Nitroxoline has excellent in vitro activity against C. auris isolates, with MICs of 0.125-1 mg/L (for comparison, the EUCAST-breakpoint for uncomplicated urinary tract infection with E. coli is ≤16 mg/L). It is an approved, well tolerated antimicrobial which achieves high urinary concentrations after oral administration and could be a useful treatment option in C. auris candiduria.

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