Candida species are common human pathogens that cause a wide range of diseases ranging from superficial to invasive candidiasis. However, basic studies focusing on the mechanisms underlying these diseases are limited. This article reviews our previous research on the mechanisms of superficial and invasive candidiasis, the virulence of Candida species, and Candida species fitness to hosts. Regarding invasive candidiasis, we focused on two types of infections: ocular candidiasis and endogenous candidiasis from the gastrointestinal tract. Using an established ocular candidiasis mouse model, along with retrospective epidemiological research, we found a strong association between Candida albicans and ocular candidiasis. Regarding endogenous candidiasis, research using Candida auris indicated that invasive strains had a higher capability for gastrointestinal tract colonization and showed greater dissemination compared with non-invasive strains. In terms of superficial candidiasis, we focused on the defense mechanism in vulvovaginal candidiasis. The results suggested that stimulated invariant natural killer T cells played a protective role against C. albicans vaginal infection and might be a therapeutic target for vulvovaginal candidiasis. Concerning Candida species fitness, we focused on environmental factors, particularly oxygen concentration, and evaluated biofilm formation under various oxygen concentrations, revealing that each Candida species favored different oxygen concentrations. In particular, Candida tropicalis showed greater biofilm formation under hypoxic conditions. Our research revealed several insights for understanding the exact mechanisms of candidiasis, which might lead to better control of Candida species infections and appropriate treatment.
Keywords: Candida species; biofilm; endogenous candidiasis; ocular candidiasis; vulvovaginal candidiasis.