Fig. 4. In vivo and in vitro loss of filamentation phenotype observations in C. auris.

a Morphologies without passage through the mouse: (1) filamentous cells were plated on YPD medium for 6 days of growth at 25 °C (no switching to the typical yeast colonies were observed, f-to-y swit. frequency < 0.01%); (2) filamentous cells were grown on YPD medium at 37 °C for 3 days, replated, and grown at 37 °C for three additional days before being replated and grown at 25 °C for 6 days (switching frequency from filamentous-to-typical yeast colonies was 1.2 ± 0.2%). b Morphologies after passage through the mouse. Filamentous cells were injected into the mouse via the tail vein. Cells recovered from tissues were grown on YPD medium at 30 °C for 2 days and then transferred at 25 °C for 5 days of incubation. Colonies shown were recovered from kidney tissues and classified as smooth (S, typical yeast) or filamentous (F). c In vivo model. Typical yeast-filament switching frequencies represent the average percentages of colonies with an alternative phenotype after passage through the animal and replating and culturing on YPD medium at 25 °C. These host-triggered switches are rare and heritable. d In vitro FC yeast-filament switches. FC yeast designation indicates a filamentation-competent form of C. auris, an intermediate cell type capable of returning from a morphologically yeast phenotype to a filamentous form following exposure to 25 °C growth conditions. The frequency of the FC yeast-to-filament switch is higher than 99% at 25 °C and the frequency of the filament-to-FC yeast switch is higher 99% at 37 °C (~1000 colonies were analyzed for each switch). Therefore, the morphological switches between the FC yeast and filamentous forms are temperature-dependent and nonheritable. e The typical yeast, FC yeast, and filamentous cell types form a three-way switching system that combines a heritable (typical yeast-to-FC yeast/filamentous) and a nonheritable (FC yeast-to-filamentous) switch. Thin and thick lines indicate low and high switching frequencies, respectively