On the Origins of a Species: What Might Explain the Rise of Candida auris?

Abstract

Candida auris is an emerging multidrug-resistant yeast first described in 2009 that has since caused healthcare-associated outbreaks of severe human infections around the world. In some hospitals, it has become a leading cause of invasive candidiasis. C. auris is markedly different from most other pathogenic Candida species in its genetics, antifungal resistance, and ability to spread between patients. The reasons why this fungus began spreading widely in the last decade remain a mystery. We examine available data on C. auris and related species, including genomic epidemiology, phenotypic characteristics, and sites of detection, to put forth hypotheses on its possible origins. C. auris has not been detected in the natural environment; related species have been detected in in plants, insects, and aquatic environments, as well as from human body sites. It can tolerate hypersaline environments and higher temperatures than most Candida species. We explore hypotheses about the pre-emergence niche of C. auris, whether in the environmental or human microbiome, and speculate on factors that might have led to its spread, including the possible roles of healthcare, antifungal use, and environmental changes, including human activities that might have expanded its presence in the environment or caused increased human contact.

Keywords: Candida auris; ecological niche; emerging infections; fungal infection; yeast.

Figure 1

Phylogenetic relationships of Candida auris with Candida vulturna strains (in bold from original publication) and other related species and genera determined from a neighbor-joining analysis of sequences of the D1/D2 domains of the LSU rRNA genes. The sequence of the type strain of Kodamaea ohmeri was the outgroup in the analysis. Bootstrap values are given at branch nodes. Bar, 0.03 changes per position. Reproduced with permission from Sipiczki M and Tap RM, Candida vulturna pro tempore sp. nov., a dimorphic yeast species related to the Candida haemulonis species complex isolated from flowers and clinical sample; published by Microbiology Society, 2016 [57].