In vivo emergence of high-level resistance during treatment reveals the first identified mechanism of amphotericin B resistance in Candida auris.

OBJECTIVE: Candida auris has emerged as a health-care-associated and multidrug-resistant fungal pathogen of great clinical concern. As many as 50% of C. auris clinical isolates are reported to be resistant to amphotericin B, but no mechanisms contributing to this resistance have been identified. Here we describe a clinical case in which high-level amphotericin B resistance was acquired in vivo during therapy and undertake molecular and genetic studies to identify and characterize the genetic determinant of resistance. METHODS: Whole-genome sequencing was performed on four C. auris isolates obtained from a single patient case. Cas9-mediated genetic manipulations were then used to generate mutant strains harbouring mutations of interest, and these strains were subsequently subjected to amphotericin B susceptibility testing and comprehensive sterol profiling. RESULTS: A novel mutation in the C. auris sterol-methyltransferase gene ERG6 was found to be associated with amphotericin B resistance, and this mutation alone conferred a >32-fold increase in amphotericin B resistance. Comprehensive sterol profiling revealed an abrogation of ergosterol biosynthesis and a corresponding accumulation of cholesta-type sterols in isolates and strains harbouring the clinically derived ERG6 mutation. CONCLUSIONS: Together these findings definitively demonstrate mutations in C. auris ERG6 as the first identified mechanism of clinical amphotericin B resistance in C. auris and represent a significant step forward in the understanding of antifungal resistance in this emerging public health threat.

Invasive Candida auris infections in Kuwait hospitals: epidemiology, antifungal treatment and outcome.

PURPOSE: Candida auris is a recently recognized yeast pathogen, which has attracted worldwide attention due to its multidrug-resistant nature and associated high mortality rates. Its persistence in hospital environment and propensity of nosocomial transmission underscores the need of continuous monitoring to prevent outbreaks. Since the first case of C. auris candidemia in May, 2014, we have identified 17 additional invasive cases, which are described here. METHODS: Identity of 17 isolates originating from proven or possible cases of invasive C. auris infection and identified as Candida haemulonii by Vitek 2 yeast identification system was confirmed by PCR-sequencing of rDNA. Information about risk factors, treatment and outcomes were retrospectively retrieved from case files. Antifungal susceptibility testing was performed by Etest. RESULTS: Thirteen cases of candidemia and 4 cases of other invasive infections were detected in 6 hospitals across Kuwait. Major risk factors included adult patients with cancer, diabetes, gastrointestinal/liver diseases and extended (> 25 days) hospital stay. All isolates were resistant to fluconazole. Additionally, 5 and 4 isolates were also resistant to voriconazole and amphotericin B, respectively. Despite antifungal treatment, 9 of 15 patients died. Most patients (n = 12) were hospitalized in 2 hospitals that are in close proximity, whereas 5 other patients were from 3 hospitals that are situated > 10 km apart. CONCLUSIONS: Occurrence of successive cases of invasive C. auris infections with resulting mortality in nine patients suggests persistence of this multidrug-resistant yeast in major hospitals in Kuwait. Early detection by continuous surveillance and enforcement of infection control measures are recommended.

Development of Echinocandin Resistance in Candida tropicalis following Short-Term Exposure to Caspofungin for Empiric Therapy.

Isolation of two echinocandin-resistant Candida tropicalis strains from endotracheal secretions of a patient following short-term exposure to caspofungin is described. Both strains exhibited resistance to echinocandins by Etest and reference broth microdilution, showing a homozygous S645P mutation within the hot spot 1 (HS-1) region of FKS1 and belonging to a unique multilocus sequence type. Other C. tropicalis isolates collected from patients in the same intensive care unit within a 60-day period were susceptible to echinocandins and contained wild-type FKS1 sequences.