Fungal Infections

Species and common names

Candida auris. C. auris is phylogenetically related to Candida haemulonii and Candida ruelliae. Previously and currently mis-identified as Candida duobushaemulonii, C. haemulonii, C. famata, C. krusei, C. lusitaniae, C. sake, Saccharomyces spp, Rhodotorula glutinis  or Kodamaea ohmeri by commercial identification systems, such as Vitek 2 and bioMérieux Industry API®/ID32.

The United States Centers for Disease Control and Prevention (CDC) recommends further testing for C. auris whenever C. haemulonii is identified or in a number of other scenarios depending on the organism reported and the method of identification. Accurate identification can be performed with VITEK MS and Bruker Biotyper matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) devices using their “research use only” databases. Molecular sequencing of the D1–D2 domain of the 28s rDNA can also identify C. auris.

The proposed taxonomic description of Candida auris sp. nov. is type strain JCM15448T= CBS10913T= DSM21092T.

Natural habitat

So far, no environmental reservoir of C. auris has been identified. A significant percentage of genes in C. auris are devoted to central metabolism, a property that is common to pathogenic Candida spp. and crucial for adaptation in diverse environments.

Geography

Four distinct clades of clinical isolates have been identified from separate geographic origins on 3 continents, suggesting a recent and nearly simultaneous emergence of different clonal populations. Several geographically related clusters have been reported from South Korea, India, South Africa, Pakistan, and hospitals in Latin America. Clonality within C. auris has been shown using AFLP, multilocus sequence typing, and MALDI-TOF MS among strains in India, South Africa, and Brazil. Next generation sequencing (NGS) has demonstrated highly related C. auris isolates in four unrelated and geographically separated Indian hospitals, suggesting that each clade exhibits low diversity.

Frequency

Candida auris is an emerging pathogen, first reported in 2009 from an ear canal infection in Japan. More recently, it has been associated with life-threatening invasive diseases such as bloodstream and wound infections globally. In a span of only seven years, this yeast which displays clonal inter- and intra-hospital transmission, has become widespread across several countries, causing a broad range of healthcare-associated invasive infections. The increasing isolation of C. auris from various clinical specimens clearly indicates its ability to colonise, invade and cause disease with varying severity.

Diseases

Candida auris has been reported to cause bloodstream infections, wound infections, and otitis. It has also been cultured from urine and the respiratory tract; however, whether isolation from these sites represents infection versus colonisation in each instance is unknown.

C. auris has been recovered in samples from blood, catheter tips, cerebrospinal fluid, bone, ear discharge, pancreatic fluid, pericardial fluid, peritoneal fluid, pleural fluid, respiratory secretions (including sputum and bronchoalveolar lavage), skin and soft tissue samples (both tissue and swab cultures), urine, and vaginal secretions. Clinically, it has been implicated as a causative agent in fungaemia, ventriculitis, osteomyelitis, malignant otitis (including otomastoiditis), complicated intra-abdominal infections, pericarditis, complicated pleural effusions, and vulvovaginitis. Much like other Candida species, there is uncertainty about the ability of C. auris to cause true respiratory, urinary, and skin and soft tissue infections despite being isolated from such samples.

While one study reported no C. auris attributable deaths among nine patients with fungemia, crude mortality rates for C. auris fungemia have otherwise ranged from 28 to 66% across a wide range of healthcare settings and patient populations.

Culture peculiarities

C. auris, on microscopy, is indistinguishable from most other Candida species. C. auris grows readily at 37–42 °C and forms light pink colonies on chromogenic agars. Differentiation of C. auris from C. haemulonii complex using CHROMagar Candida supplemented with Pal's medium

Unlike C. haemuloniiC. auris does not form pseudohyphae however some strains can form rudimentary pseudohyphae on cornmeal agar. C. auris is capable of forming biofilms and adhering to catheter material, although not to the same degree as Candida albicans.

Antifungal resistance (instrinsic and acquired)

Almost all strains of C. auris are resistant to fluconazole and many are resistant to amphotericin B, voriconazole, echinocandins and flucytosine.

There are no Clinical and Laboratory Standards Institute (CLSI) or European Committee for Antimicrobial Susceptibility Testing (EUCAST) defined breakpoints for C. auris susceptibility. Fluconazole (tentative MIC breakpoint ≥32) is associated with high minimum inhibitory concentrations (MICs) with MIC50 results between 64 and 128 mg/L and MIC90 results between 64 and 256 mg/L by CLSI microbroth dilution, in four studies. Echinocandins (tentative MIC breakpoint ≥4 for anidulafungin and micafungin, ≥2 for caspofungin) appear to be most active in these studies with favorable results for anidulafungin (MIC50 range 0.125–0.5, MIC90 range 0.5–1), caspofungin (MIC50 0.25–0.5, MIC90 1), and micafungin (MIC50 0.125–0.25, MIC90 0.25–2). Amphotericin B (tentative MIC breakpoint ≥2) susceptibility testing exhibits a wider range of MIC results (MIC50 0.5–1, MIC90 2–4) and is likely less reliable as empiric therapy. In comparison to CLSI microbroth dilution, similar MIC50 and MIC90 results can likely be obtained by the EUCAST method.  Caution should be used when interpreting Etest and Vitek antifungal susceptibility testing results.

Biosafety level 2

Industrial use None

 

Images

Candida auris on agar

Candida auris colonies on agar (picture courtesy of the Centers for Disease Control and Prevention)

 

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