Oropharyngeal candidiasis and resistance to antifungal drugs in patients receiving radiation for head and neck cancer

Oropharyngeal candidiasis is a common infection in patient receiving radiotherapy for head and neck cancer. Accurate and rapid identification of candida species is very important in clinical laboratory, because the incidence of candidiasis continues to rise after radiotherapy. The genus Candida has about 154 species that show different level of resistance to antifungal drugs and have high degree of phenotypic similarity. The aim of this study was to investigate oral yeast colonization and infection and resistance to antifungal drugs in these patients. Thirty patients receiving a 6-week course of radiation therapy for treatment of head and neck cancer at the Oncology Unit in Shafa Hospital, in 2008, were enrolled in the study. Specimens from patients were cultured weekly for Candida. All isolates were plated on CHROM agar and RPMI-based medium. They were subcultured and submitted for antifungal susceptibility testing (nystatin, fluconazole, clotrimazole and ketoconazole) and molecular typing. Infection (clinical and microbiological evidence) occurred in 50% of the patients and Candida colonization (only microbiological evidence) occurred in 70% of subjects in the first week. Candida albicans alone was isolated in 94.9% of patient visits with positive cultures. Candida tropicalis was isolated from 5.1% of patient visits with positive cultures. All isolates were susceptible to nystatin, but did not respond to the other antifungal drugs The irradiation-induced changes of the intraoral environment such as xerostomia lead to increased intraoral colonization by Candida species. All yeast isolates were susceptible to nystatin. Thus prophylactic therapy with nystatin should be considered for these patients.