CHK1 from the two-component system of Candida albicans regulates the antifungal activity and resistance of quaternary ammonium salts

Quaternary ammonium salts (QAS) are wildly used to eradicate the microorganisms in the environment and pathogens in infectious diseases. However, the antifungal mechanisms are still not clear. Here, we aimed to evaluate the antifungal and resistant mechanism of a QAS named DMADDM. DMADDM could inhibit both azole sensitive and resistant Candida albicans strains. We then successfully induced DMADDM-resistant strains with that the MICs was enhanced for 2 or 4 folds. The genomes of four DMADDM resistant isolates and wild type strain were sequenced. CHK1 gene from the two component system of C. albicans was one of the most frequent mutated genes in these resistant strains and the chk1 delete mutant become resistant to DMADDM indicating the important role of CHK1 gene in the antifungal actions and resistance of QAS. DMADDM was capable to bind the fungal cell membrane to cause the depolarization. It then inhibited CHK1 gene expression and downregulated the downstream ROS scavenging genes to increase the ROS accumulation, and furtherly induced the cell apoptosis in wild type and CHK1 complementary strains to kill C. albicans. However, the chk1 delete mutant can reduce the fungal cell binding to DMADDM and the depolarization of the cell membrane caused by DMADDM. DMADDM also failed to affect the ROS scavenging genes expression and ROS accumulation in the chk1 delete mutant, in line with the resistant ability of chk1 delete mutant to DMADDM. The role of CHK1 gene in the antifungal activity and resistance of DMADDM were then proved in an oropharyngeal candidiasis murine model. DMADDM could treat the oral candidiasis caused by C. albicans wild type and CHK1 complementary strains by reducing the infected area and fungi loads. But DMADDM failed in the treatment of oral infection caused by chk1 delete mutant. In this study, we identified the antifungal and resistant mechanism of QAS for the first time and suggested that the application of QAS should be reconsidered for its resistance in microbes.