Suppression of Mixed Candida Biofilms with an Iodine Oral Rinse

Objective: The purpose of this study was to evaluate the effectiveness of oral candidiasis treatments in inhibiting metabolic activities of yeast cells in mixed biofilms formed by C. albicans and C. glabrata. The products tested included four concentrations of an iodine-based oral rinse (Iocide), chlorhexidine gluconate and fluconazole. Methods: C. albicans SC5314 and C. glabrata CBS138 were propagated to 1x10⁶ cells/ml. Mixtures of C. albicans to C. glabrata were prepared in the following ratios: 100:0; 99:1; 67:33; 33:67; and 0:100. One-tenth ml of each suspension was added per well in 96 well microtiter plates that were incubated at 37°C for 24hr to allow for biofilm formation. The following treatments were added to groups of 8 wells: oral rinse formulations (0.01%, 0.05%, 0.07%, or 0.1% iodine), placebo oral rinse (no iodine), PBS (cell control), chlorhexidine gluconate oral rinse (0.12%) or fluconazole (10mg/ml oral suspension). Exposure time of each challenge was 60 sec at 22°C. Metabolic activity was determined via XTT reduction assay. Results: An exposure time of only 1 min was sufficient to reduce metabolic activities of biofilm cells by ≥97% with the formulation tested containing the highest concentration (0.1%) of iodine. The oral rinse formulations containing 0.05%, 0.07%, or 0.1% iodine demonstrated greater reduction of metabolic activity than either chlorhexidine gluconate or fluconazole for all ratios of C. albicans/C. glabrata tested. A dose-response was observed as increased levels of inhibition of cell metabolic activities corresponded to increasing iodine concentrations. In addition, cells in mixed Candida spp biofilms containing increasing proportions of C. glabrata exhibited increasing susceptibility to the iodine-based formulations. Conclusions: Iodine-base oral rinse formulations are effective in reducing metabolic activities of cells in mixed C. albicans/C. glabrata biofilms. Iodine-based oral formulations were more effective than both chlorhexidine gluconate and fluconazole in this assay. Funding provided by 1R43DE017301-01.