# Molecular Techniques and Target Selection for the Identification of _Candida_ spp. in Oral Samples
## 2 Epidemiology of _Candida_ Infections  
Several Candida species are commensal and colonize the human skin and mucosal surfaces either in a free cell form or in a biofilm. Biofilms, a dynamic community of surface-associated microbes, are protected by an extracellular polymeric matrix and are strongly related to Candida's infection [16; 17; 18].  
Candida albicans is considered the most common Candida species associated with infection in humans, being often linked to life-threatening situations in elderly, immunocompromised, or critically ill patients [19; 20; 21]. The increasing number of invasive surgical procedures, the extensive use of broad-spectrum antimicrobials, and the prevalence of clinical illness, especially in infant and elderly populations, are some of the reasons for the globally increased incidence of candidemia [22]. The Centers for Disease Control and Prevention (CDC) estimate that approximately 25,000 cases of candidemia occur in the United States of America each year [23]. Non-C. albicans species cause approximately two-thirds of candidemia cases in the USA [24], with C. auris being considered a relevant emergent pathogen [15]. In 2019, an epidemiologic meta-analysis was performed in Europe, showing the increasing incidence rate of candidemia with a higher proportion of Candida spp. other than C. albicans [25].  
Mortality among patients with invasive candidiasis is as high as 40%, even when receiving antifungal therapy [22; 26]. High mortality rates in Candida infections are in part justified by diagnostic inaccuracy (i.e., incorrect identification at the species level and of the drug resistance profile), which may compromise the administration of adequate antifungal therapies and ultimately lead to the patient's death [27; 28; 29]. The criteria for initiating Candida antifungal therapy remains poorly specified and often contributes to the widespread prescription of antifungal drugs with no regard for toxicity risks, resistance selection, and unnecessarily high costs of antifungal treatments [30; 31; 32; 33].  
Oral candidiasis (\"thrush\") is an opportunist oral mucosa fungal infection [1] that can result in serious health complications and ultimately spread through the bloodstream and lead to candidemia. Furthermore, this infection is commonly associated with elderly patients, frequently leading to longer treatments and higher costs for the health systems. Regarding the diagnosis of oral candidiasis, saliva has been used as a target sample, being already used in the diagnosis of other oral and systemic diseases, such as oral cancer [34; 35] and SARS-CoV-2 [36].  
The antifungal agents in use for the treatment of oral candidiasis are polyenes (nystatin and amphoteric B), allyamines (terbinafine), and azoles (fluconazoleide, itraconazole, voriconazole, and ketaconazole). A major concern is the misuse of antimycotic agentscontributing to antifungal resistance in Candida (Table S1). [PERSON] and colleagues characterized Candida oral isolates and showed that most C. glabrata isolates are susceptible to niconazole and nystatin, but resistant to funconazole and itraconazole. In the same study, Candida parapysilosis isolates were susceptible to fluconazole while azide cross-resistance to niconazole and itraconazole was noted [37]. Increased resistance to antifungal compounds, especially to azoles and to amphoteric B, was already reported [38; 39; 40; 41]. All isolates investigated by [PERSON] and colleagues (2011) were susceptible to amphoteric B, and 50% of the C. glabrata isolates were resistant to fluconazole [42]. The specific species of Candida responsible for candidemia and Candida spp. that cause oral candidiasis have different susceptibility patterns. Interestingly, Candida krusei susceptibility patterns show multidrug resistance patterns when they are isolated from both oral and blood samples (Table 1).