Boric Acid and Persisters in Candida Albicans

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Medicine and Health Sciences


Persisters are a special group of quiescent and phenotypically unique cells in a given microbial population that survive antimicrobial insults or stresses but retain properties of the original population. Persisters have been characterized and studied in bacteria; however, little work exists on evaluating the persister phenotype in yeast. Previous research with 12 clinical isolates of Candida albicans elucidated antifungal properties of boric acid (BA) as a potential treatment alternative for vaginal candidiasis. Objective: This project aimed to identify and quantify C. albicans persister colonies that may appear when exposed to BA, antifungals and BA-single antifungal combinations. Methods: C. albicans was grown in RPMI 1640 media, experimentally modified to 1% BA, 5μg/mL miconazole, 2μg/mL amphotericin B or 1μg/mL caspofungin. The combination conditions were at the same concentrations. Growth was quantified with flow-cytometry and CFUs counted on agar. Persisters were measured as a ratio of CFUs to flow events per μL. Results: Miconazole and amphotericin B both decreased percent persisters at 24h (0.92% and 1.88%) and 48h (3.74% and 2.37%) when compared to BA alone at 24h and 48h (33.34% and 119.11%) while caspofungin increased persisters at 24h and decreased at 48h (138.00% and 65.82%). Combination conditions decreased percent persisters when compared to BA and respective single antifungals alone at both 24h (BAMiconazole, 1.20%, BA-Amphotericin B, 0.46%, BA-Caspofungin, 17.11%) and 48h (1.60%, 0.43%, 13.30%). Conclusion: BA appears to have a synergistic effect on growth inhibition and persister colony formation. Further work is needed to elucidate if these colonies have a unique persister phenotype or are only survivors from antifungal insult. This work shows that BA may be a potential therapeutic to inhibit persister formation, a target separate from antifungal resistance.


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