Candida auris Phenotypic Heterogeneity Determines Pathogenicity In Vitro

Abstract

Candida auris is an enigmatic yeast that provides substantial global risk in health care facilities and intensive care units. A unique phenotype exhibited by certain isolates of C. auris is their ability to form small clusters of cells known as aggregates, which have been to a limited extent described in the context of pathogenic traits. In this study, we screened several nonaggregative and aggregative C. auris isolates for biofilm formation, where we observed a level of heterogeneity among the different phenotypes. Next, we utilized an RNA sequencing approach to investigate the transcriptional responses during biofilm formation of a nonaggregative and aggregative isolate of the initial pool. Observations from these analyses indicate unique transcriptional profiles in the two isolates, with several genes identified relating to proteins involved in adhesion and invasion of the host in other fungal species. From these findings, we investigated for the first time the fungal recognition and inflammatory responses of a three-dimensional skin epithelial model to these isolates. In these models, a wound was induced to mimic a portal of entry for C. auris. We show that both phenotypes elicited minimal response in the model minus induction of the wound, yet in the wounded tissue, both phenotypes induced a greater response, with the aggregative isolate more proinflammatory. This capacity of aggregative C. auris biofilms to generate such responses in the wounded skin highlights how this opportunistic yeast is a high risk within the intensive care environment where susceptible patients have multiple indwelling lines. IMPORTANCE Candida auris has recently emerged as an important cause of concern within health care environments due to its ability to persist and tolerate commonly used antiseptics and disinfectants, particularly when attached to a surface (biofilms). This yeast is able to colonize and subsequently infect patients, particularly those that are critically ill or immunosuppressed, which may result in death. We have undertaken analysis on two different phenotypic types of this yeast, using molecular and immunological tools to determine whether either of these has a greater ability to cause serious infections. We describe that both isolates exhibit largely different transcriptional profiles during biofilm development. Finally, we show that the inability to form small aggregates (or clusters) of cells has an adverse effect on the organism’s immunostimulatory properties, suggesting that the nonaggregative phenotype may exhibit a certain level of immune evasion.

Virulence ofCandida aurisfrom different clinical origins inCaenorhabditis elegansandGalleria mellonellahost models

“…Although C. auris biofilms are thinner than those of C. albicans [ 46 ], the capacity of C. auris to form a biofilm has been clearly associated with a lower antifungal susceptibility [ 16 , 47 ]. The ability of C. auris to form a biofilm has been reported for both aggregating and non-aggregating phenotypes [ 12 ]. Biomass values obtained in the current study were similar to those reported by Sherry et al (2017) [ 22 ].…”

“…However, these authors reported the highest biofilm-forming capacity for non-aggregating isolates. Brown and coworkers [ 12 ] also detailed differences in gene expression between both phenotypes: genes related to cellular components (membrane and cell wall constituents) were upregulated in isolates with aggregating phenotype whereas genes related to biological processes and metabolic functions were expressed higher in non-aggregating isolates. Moreover, Short et al (2019) [ 48 ] suggested that the ability of C. auris to form cellular aggregates increases survival of the yeast, which coincided with the upregulation of biofilm-associated genes.…”

“…In addition, in C. albicans , the ability to produce biofilm has been associated with the expression of secreted aspartyl proteinases [ 49 ]. Genes involved in biofilm formation and in the production of phospholipase, proteinase and hemolysin activity have been reported in C. auris , with genes involved in cell adhesion and invasion ( ALS and SAP families) showing stronger expression in aggregating than in non-aggregating isolates [ 8 , 12 , 13 , 50 ]. However, in the present study, phospholipase and proteinase activities were not detected in any clinical isolate nor any hemolytic activity was observed (Table S1).…”

“…Expression of phospholipase, proteinase, and hemolytic activities, adherence and biofilm formation, antifungal drug and environmental stress resistance are described among the most relevant virulence traits [ 9–11 ]. However, the knowledge on C. auris virulence remains scarce and further studies are required to understand its pathogenic behavior, which has been reported to be substantially variable among clades [ 12 ]. Currently, about 30 studies have incorporated in vivo models in the analysis of C. auris virulence, murine models being the most widely used [ 13–18 ].…”

“…Recently, two different phenotypes, aggregating and non-aggregating (single-cell phenotype), have been described among C. auris clinical isolates; the latter presenting a higher virulence [ 21 , 22 , 26 ]. Transcriptional profiles were evidently different between isolates with these two different phenotypes, and differences in the host response, depending on whether there is loss of tissue integrity, were also reported [ 12 ]. Although attempts have been made to correlate the site of origin of clinical isolates with their virulence in different Candida species [ 34–37 ], no association has been reported between the pathogenicity of C. auris and the origin of clinical specimens.…”