Candidiasis is the most common fungal infection of the oral cavity, and is caused by Candida spp. Previously, it was thought that between 35–80% of the population harbor Candida in the oral cavity in the world. The most common oral species is Candida albicans, which is estimated to be present in 80% of oral fungal isolates (Lewis and Williams, 2017, Talapko et al., 2021). Various factors can disrupt oral homeostasis, changing to abnormal flora (dysbiosis) and leading to microbial overgrowth and the expression of virulence factors (Lewis and Williams, 2017, Zdanavičienė et al., 2017). Infections are typically opportunistic and influenced by host factors such as xerostomia, poor denture cleaning, and topical steroid preparations (Oouchi et al., 2015). In addition, infection can become established when systemic defense mechanisms are abnormal, such as long-term administration of antimicrobials, steroids, anti-cancer drugs, or immunosuppressive drugs, and in immunocompromised patients due to AIDS, diabetes mellitus, or aging (Mane et al., 2012, Soysa et al., 2006, Suryana et al., 2020).

Three forms of oral candidiasis are known to exist: pseudomembranous candidiasis is characterized by a layer of detachable white moss; erythematous candidiasis is smooth and erythematous; and hypertrophic candidiasis has a thickened and hardened mucosal epithelial layer in a speckled pattern because of chronicity (Jayampath Seneviratne et al., 2015). Clinical symptoms often include pain (mainly on the tongue), xerostomia, dysgeusia (such as tasting bitterness), and oral discomfort (such as a sticky sensation). Candidiasis is typically treated with antifungal drugs; however, there are many cases in which this is ineffective. Together with the nature and prevalence of C. albicans, the existence of antifungal-resistant candidiasis suggests that there may be key differences between strains. Although there are many reports on the characteristics of C. albicans derived from systemic or oral candidiasis, there have been few reports comparing the virulence-related activities of Candida in patients with oral candidiasis to those in healthy individuals. In addition, although it has been reported that there are regional differences in genotypes and pathogenicity of C. albicans (Mccullough et al., 1999), their differences remain unknown in Hokkaido, the northernmost prefecture in Japan. Therefore, this study aimed to elucidate the differences in genotypes and virulence-related activities between C. albicans strains from patients with oral and non-oral candidiasis in Hokkaido.