Candida auris Forms High-Burden Biofilms in Skin Niche Conditions and on Porcine Skin

Abstract

Emerging pathogen Candida auris causes nosocomial outbreaks of life-threatening invasive candidiasis. It is unclear how this species colonizes skin and spreads in health care facilities. Here, we analyzed C. auris growth in synthetic sweat medium designed to mimic axillary skin conditions. We show that C. auris demonstrates a high capacity for biofilm formation in this milieu, well beyond that observed for the most commonly isolated Candida sp., Candida albicans The C. auris biofilms persist in environmental conditions expected in the hospital setting. To model C. auris skin colonization, we designed an ex vivo porcine skin model. We show that C. auris proliferates on porcine skin in multilayer biofilms. This capacity to thrive in skin niche conditions helps explain the propensity of C. auris to colonize skin, persist on medical devices, and rapidly spread in hospitals. These studies provide clinically relevant tools to further characterize this important growth modality.IMPORTANCE The emerging fungal pathogen Candida auris causes invasive infections and is spreading in hospitals worldwide. Why this species exhibits the capacity to transfer efficiently among patients is unknown. Our findings reveal that C. auris forms high-burden biofilms in conditions mimicking sweat on the skin surface. These adherent biofilm communities persist in environmental conditions expected in the hospital setting. Using a pig skin model, we show that C. auris also forms high-burden biofilm structures on the skin surface. Identification of this mode of growth sheds light on how this recently described pathogen persists in hospital settings and spreads among patients.

Keywords: Candida auris; biofilm; pathogenicity; porcine; skin; sweat; transmission.

FIG 1

C. auris forms high-burden biofilms in synthetic sweat medium. (a) Candida biofilms were grown in RPMI-MOPS or synthetic sweat medium for 24 h, and biofilm burden was measured by absorbance at 600 nm. C. auris biofilm density was compared to that of C. albicans in each media by Student's t test, *, P < 0.05, standard errors of the means shown, n = 3. (b) Candida biofilms were grown on coverslips (24 h) and imaged with scanning electron microscopy. Bars, 10 μm and 1 μm for ×2,000 and ×10,000 magnification images, respectively. (c) Candida biofilms were grown in various concentrations of synthetic sweat medium for 24 h, *, P < 0.05 by Student's t test at each concentration, standard errors of the means shown, n = 3. (d and e) Candida biofilms were subjected to 24 h of desiccation, and viable burdens were assessed by plating of serial dilutions of disrupted biofilms after 7 or 14 days, *, P < 0.05 by Student's t test, standard errors of the means shown, n = 6; n.d., not detected.

FIG 2

C. auris effectively colonizes porcine skin. (a) Porcine skin samples were placed in DMEM supplemented with 10% FBS and set in paraffin to separate the epidermal surface from the liquid medium. Candida cells suspended in synthetic sweat medium were inoculated on the epidermal surface. (b) Candida cultures were suspended in synthetic sweat medium inoculated on the surface of porcine skin samples. Following 24 h of incubation, Candida growth on the hair and skin surface was enumerated via CFU counts. *, P < 0.05 by Student's t test, standard errors of the means shown, n = 4. (c) Candida biofilms were grown on porcine skin samples and imaged with scanning electron microscopy. Bars, 100 μm, 20 μm, and 10 μm for ×100, ×500, and ×2,000 magnification, respectively.