Stress Response in Candida albicans Induced by Boric Acid

Background: Topical boric acid preparations have been employed in treatment of Candida-associated vaginal infections resistant to typical antifungal treatments; however, a mechanism of boric acid’s antifungal properties is not fully understood.

Aims: Investigate the antifungal properties of boric acid associated with Candida albicans and cell number and geometry through flow cytometry.

Study Design: Twelve clinical isolates of Candida albicans were grown in Sabouraud broth with varying concentrations of boric acid followed by measurements of cell characteristics.

Methodology: Absolute counts, cell size data, and fluorescence of test organisms were determined by flow cytometry. All microbial count and growth experiments were conducted in at least duplicate and averages were reported.

Results: Each of the twelve strains showed susceptibility to boric acid with ED50 values below 2400 mg/L. Boric acid decreased cell survival in growth media and distilled water (P<0.05), but disintegration of cells occurred in boric acid and water but not in water alone. Boric acid reduced cell volume implying apoptosis which was supported by annexin V staining. Cell involution and cell number were used to determine relative biomass which showed that biological effects were apparent even at 0.05% (500 mg/L). Mean autofluorescence of test organisms grown in boric acid increased in a dose-dependent manner. Inhibition of catalase could contribute to proapoptotic activity making Candida albicans more susceptible to ROS internally.

Conclusion: Boric acid was shown to effectively decrease cell size, induce cell autofluorescence, decrease catalase activity, and initiate programmed cell death. Further experimentation should investigate specific mechanisms of boric acid-induced apoptosis and its role in altering catalase activity.