Efficacy of cold atmospheric plasma and fluconazole against resistant Candida species in oropharyngeal candidiasis patients

Oropharyngeal candidiasis (OPC) remains the most common opportunistic fungal infection affecting patients with head and neck cancer, and the growing challenge of antifungal resistance has become a critical concern in recent years. In this study, the effect of cold atmospheric plasma (CAP) in combination with fluconazole (Flu) was investigated in 15 clinical Candida strains comprising C. albicans and C. tropicalis (fluconazole-resistant) and C. glabrata (susceptible dose-dependent) from oropharyngeal candidiasis (OPC) in patients with head and neck cancer. A CAP jet system using a helium–oxygen mixture (98:2 v/v) was utilized. Fungal growth, biofilm formation, and ergosterol content were evaluated after treatment with the combination of fluconazole and CAP in all three Candida species. The expression of HWP1, ERG11, and SAP2 genes was evaluated in all Candida species after CAP therapy. CAP treatment induced time-dependent reductions in fungal viability across all species ( P < 0.0001), with C. glabrata demonstrating the highest susceptibility and C. tropicalis the lowest. Ergosterol content decreased maximally at 120s, with inhibition rates of 72.13%, 59.94%, and 68.07% for C. albicans, C. tropicalis, and C. glabrata , respectively, followed by partial recovery at 150s. CAP monotherapy significantly reduced planktonic growth and biofilm formation; however, combination with fluconazole yielded no synergistic or additive effects (ns for all comparisons). Gene expression analysis revealed species-dependent transcriptional responses; C. albicans showed maximal downregulation at 90s, C. glabrata exhibited the most sustained suppression, while C. tropicalis demonstrated relative transcriptional resilience. CAP exerts potent antifungal activity against fluconazole-resistant Candida clinical isolates and downregulation of virulence and resistance genes, with species-specific susceptibility patterns. The lack of synergistic interaction with fluconazole indicates that CAP operates via pathways independent of fluconazole. Further in vivo research is required to harness its potential as a therapeutic strategy.