Superoxide Dismutases Are Involved in Candida albicans Biofilm Persistence against Miconazole

Abstract

ABSTRACTWe investigated the cellular mechanisms responsible for the occurrence of miconazole-tolerant persisters inCandida albicansbiofilms. Miconazole induced about 30% killing of sessileC. albicanscells at 75 μM. The fraction of miconazole-tolerant persisters, i.e., cells that can survive high doses of miconazole (0.6 to 2.4 mM), in these biofilms was 1 to 2%. Since miconazole induces reactive oxygen species (ROS) in sessileC. albicanscells, we focused on a role for superoxide dismutases (Sods) in persistence and found the expression of Sod-encoding genes in sessileC. albicanscells induced by miconazole compared to the expression levels in untreated sessileC. albicanscells. Moreover, addition of the superoxide dismutase inhibitorN,N′-diethyldithiocarbamate (DDC) toC. albicansbiofilms resulted in an 18-fold reduction of the miconazole-tolerant persister fraction and in increased endogenous ROS levels in these cells. Treatment of biofilms ofC. albicansclinical isolates with DDC resulted in an 18-fold to more than 200-fold reduction of their miconazole-tolerant persister fraction. To further confirm the important role for Sods inC. albicansbiofilm persistence, we used a Δsod4Δsod5mutant lacking Sods 4 and 5. Biofilms of the Δsod4Δsod5mutant contained at least 3-fold less of the miconazole-tolerant persisters and had increased ROS levels compared to biofilms of the isogenic wild type (WT). In conclusion, the occurrence of miconazole-tolerant persisters inC. albicansbiofilms is linked to the ROS-detoxifying activity of Sods. Moreover, Sod inhibitors can be used to potentiate the activity of miconazole againstC. albicansbiofilms.