Molecular Mechanism of Action of HOCl from Neutral-pH Electrolysed Oxidising Water Against Candida albicans.

Chemical disinfection of removable acrylic dental prostheses minimizes the risk of denture stomatitis caused by the opportunistic fungal pathogen Candida albicans. We previously reported that neutral-pH electrolysed oxidising water (EOW), a hypochlorous acid (HOCl)-based biocide, is effective at inhibiting C. albicans biofilm formation on denture resins. Knowledge about the mechanism of action of EOW on C. albicans is lacking. This study investigated the molecular mechanism of action of neutral-pH EOW against C. albicans cells that were incubated with sub-inhibitory concentrations of EOW-HOCl (treatment with 0.125× MIC90 EOW-HOCl (15 µM; T0.125) or treatment with 0.5× MIC90 EOW-HOCl (59 µM; T0.5)). RNA-sequencing (RNA-seq) was used to identify differentially expressed genes (DEGs) which were validated by qRT-PCR. Ninety-five DEGs were identified between the treated and untreated cells after a 60 min exposure. A moderate sub-inhibitory EOW-HOCl concentration (T0.125) caused significant upregulation (log2 fold change > +2) of genes responsive to oxidative stress (EBP1, GAP6, PRN1, HSP21), weak organic acid stress (PRN1), and heat-shock (HSP21). A higher sub-inhibitory concentration (T0.5) caused a significant downregulation of most DEGs (notably, -1.9 to -3 log2 fold reduction in SUT1, HNM3, STP4 expression), cessation of growth, and an upregulation of genes involved in ammonia transport, carbohydrate metabolism, and the unfolded protein and apoptotic response pathways (ATO2, IRE1). Our findings reveal HSP21 and PRN1 to be possible key players in protecting C. albicans cells against HOCl, a natural biocide of the innate immune system.