Candida auris is a species of fungus that grows as yeast. It is one of the few species of the genus Candida which cause candidiasis in humans. Often, candidiasis is acquired in hospitals by patients with weakened immune systems. C.auris can cause invasive candidiasis (fungemia) in which the bloodstream, the central nervous system, and internal organs are infected. It has attracted widespread attention because of its multiple drug resistance. Treatment is also complicated because it is easily misidentified as other Candida species.
Candida auris was first described in 2009 after it was isolated from the ear canal of a 70-year-old Japanese woman at the Tokyo Metropolitan Geriatric Hospital in Japan. In 2011, South Korea saw its first cases of disease-causing C.auris. Reportedly, this spread across Asia and Europe, and first appeared in the U.S. in 2013.
DNA analysis of four distinct but drug-resistant strains of Candida auris indicate an evolutionary divergence taking place at least 4,000 years ago, with a common leap among the four varieties into drug-resistance possibly linked to widespread azole-type antifungal use in agriculture. However, explanations for its emergence remain speculative.
Identification and morphology
First identified in 2009, Candida auris is a species of ascomycetous fungus of the genus Candida that grows as a yeast. Its name comes from the Latin word for ear, auris. It forms smooth, shiny, whitish-gray, viscous colonies on growth media. Microscopically, cells are ellipsoid in shape.
Clinical significance
Candida auris has attracted increased clinical attention because of its multiple drug resistance.
In vitro, more than 90% of C.auris isolates are resistant to fluconazole and a range of 3–73% of C.auris isolates are resistant to voriconazole, while other triazoles (posaconazole, itraconazole, and isavuconazole) display better activity. Of isolates, 13% to 35% were reported resistant to amphotericin B; however, most isolates are susceptible to echinocandins.
Treatment is complicated because C.auris is easily misidentified as various other Candida species. A brief outline of its clinical relevance , understandable by general audiences, was published by the Center for Infectious Disease Research and Policy at the University of Minnesota.
According to papers published from 2011 to 2016, mortality of people with C.auris bloodstream infections (BSI) ranged from 30 to 60%. Many of these people had other serious illnesses and conditions (comorbidities) that increased their risk of death.
Vaccine development
there is no human vaccine against Candida auris. Experiments involving the NDV-3A vaccine have successfully immunized mice against the fungus. The vaccine also improved the protective efficacy of the antifungal drug micafungin against C. auris infection in the mouse bloodstream.
Genome
Several draft genomes from whole genome sequencing have been published. C.auris has a genome size of 12.3–12.5 with a GC-content of 44.5–44.8%. The C.auris genome was found to encode several genes for the ABC transporter family, a major facilitator superfamily, which helps to explain its multiple drug resistance. Its genome also encodes virulence-related gene families such as lipases, oligopeptide transporters, mannosyl transferases and transcription factors which facilitate colonization, invasion, and iron acquisition. Another factor contributing to antifungal resistance is the presence of a set of genes known to be involved in biofilm formation.
More studies are needed to determine whether the phylogenetic divergence of C.auris clones exhibits region-specific patterns of invasiveness, virulence, and/or drug resistance.
Epidemiology
Geographical differentiation
The phylogenetics of C.auris suggest distinct genotypes exist in different geographical regions with substantial genomic diversity. A variety of sequence-based analytical methods have been used to support this finding.
Whole genome sequencing and analyses of isolates from Pakistan, India, South Africa, Venezuela, Japan, and previously sequenced C.auris genomes deposited in the National Center for Biotechnology Information's Sequence Read Archive identified a distinct geographic distribution of genotypes. Four distinct clades separated by tens of thousands of single-nucleotide polymorphisms were identified. The distribution of these clades segregated geographically to South Asia (India and Pakistan), South Africa, Venezuela, and Japan with minimal observed intraregion genetic diversity.