Oral Candida Colonisation in Radiotherapy-Treated Head and Neck Cancer Patients: Prevalence, Species Diversity and Antifungal Resistance Compared with Healthy Controls

Head and neck cancer (HNC) patients frequently experience alterations in the oral environment following radiotherapy, including xerostomia and impaired mucosal integrity, which may favour fungal overgrowth. This study aimed to characterise oral Candida colonisation in radiotherapy-treated HNC patients and compare it with that of healthy individuals. Unstimulated saliva samples from 61 HNC patients and 100 controls were cultured on chromogenic agar, and isolates were identified using API 20C AUX or MALDI-TOF. Salivary flow was measured to quantify xerostomia. A representative subset of isolates (10 per group) underwent antifungal susceptibility testing by disk diffusion according to CLSI/EUCAST criteria. Candida colonisation was significantly higher in HNC patients than in controls (64.6% vs. 20%, p < 0.001), with greater species diversity and increased detection of non-albicans yeasts, including C. tropicalis, C. parapsilosis, C. glabrata, and C. krusei. All HNC patients exhibited reduced salivary flow. Azole resistance was more frequent among HNC isolates (26%) than among controls (10%), whereas all isolates remained susceptible to amphotericin B and nystatin. These findings indicate that radiotherapy-associated xerostomia substantially alters the oral mycobiota and underscore the importance of routine species-level identification and antifungal susceptibility testing in HNC patients to guide clinical decision-making.