Replicative Aging in Candida auris Has an Effect on Antifungal Resistance

BACKGROUND: Candida auris can colonize patients for a prolonged time causing life-threatening systemic infections. Replicative aging is the result of asymmetric division, which cause phenotypic changes between mother and daughter cells. We have previously published that older Cryptococcus neoformans and C. glabrata cells exhibit enhanced resistance to antifungals including fluconazole (FLC), five flucytosine (5FC), and sub-therapeutic amphotericin B (AMB). Additionally, they are more resistant to macrophage and neutrophil killing. This is relevant because older fungal cells accumulate in chronic infections. We hypothesized that older C. auris cells would also exhibit enhanced resistance to phagocytic cells and can alter drug resistance. METHODS: Magnetically labeled cells were grown for 10 generations (Gen) and then were isolated from daughter cells by magnetic column separation. Transmission electron microscopy (TEM) was performed to measure their cell wall thickness. Standard in vitro killing assays were performed with human neutrophils. In vivo virulence was compared in a Galleria injection model. Minimum inhibitory concentration to the antifungals was performed by CSLI methods. Rhodamine 6G (R6G), which is a fluorescent substrate for ABC-transporters, was used to measure efflux. RESULTS: In C. auris, 10 Gen old cells are larger than younger cells (0–3 Gen) and exhibit a thicker cell wall on TEM. The older cells are significantly more resistant to neutrophil killing (24.5% vs. 51.6%, P < 0.05 by paired t-test)). Eleven distinct isolates manifest variable virulence in the Galleria infection model (range 1–8 days). In C. auris, 10 Gen cells were significantly more virulent than 0 Gen cells (2 days vs. 4 days). Most (8 of 11) isolates were highly resistant to FLC and showed high efflux of R6G, whereas the three FLC sensitive isolates showed low efflux of R6G. Using these methods, we observed significant (1.5 to 2.0 fold, P < 0.05) increase in efflux activity of older cells in both sensitive and resistant isolates. CONCLUSION: In C. auris replicative aging is associated with enhanced resistance to phagocytic killing, increased cell body size, and cell wall thickness. Aging also enhances efflux activity and thus may contribute even further to antifungal resistance. DISCLOSURES: All authors: No reported disclosures.