Introduction: A hypochlorous acid based wound cleanser was able to disrupt biofilms of bacterial pathogens in previous experiments. However, there have been questions regarding its efficacy in eliminating yeast, especially considering variations in susceptibility of clinical isolates of Candida auris to commonly used antifungal medications. The purpose of this study was to determine potency and limitations of this solution in clearing yeast isolates with different levels of tolerance to Amphotericin B.
Methods: Three Candida auris isolates with variable minimum inhibitory concentrations (MIC) were used to represent an Amphotericin B sensitive, responsive, and resistant strain. The Hypochlorous acid-based Wound Solution (HWS) was tested using two assays. The first was the agar well diffusion assay in which 1x10^9 cells/ml were inoculated onto agar plates containing a well which was filled with 100 µl of HWS, or control saline or 1% amphotericine solutions as positive or negative control plates. Plates were incubated for 24 hours. Inhibition of yeast around the well was observed. The second assay was performed by incubating yeast cultures at 5 different concentrations with HWS, saline, or 1% amphotericin in 10x serial dilutions. Viability of yeast was evaluated by growing an aliquot of treatment mix on agar plates and also examining yeast proliferation by incubating at 30 ºC and assessing turbidity by gross observation and cell counts under the microscope.
Results: Treatment with HWS prevented growth of yeast in the area around the well in all strains. These results were similar to Amphotericin B (1%) treated plates, however the efficacy of Amphotericin was stronger, Treatment of all isolates of yeast cultures with HWS at a 1:1 mix in liquid media for 30 min at RT did not result in reduction of yeast based on the turbidity. Early time points in HWS treated cultures showed slower growth of yeast compared to saline-treated cultures. In agreement with the turbidity and cell count results, viability on agar plates after treatment with HWS at 1:1 mix with ≈2x10^5 cell/mL mix showed colonies. No growth was seen in plates inoculated with culture treated with Amphotericin. However, treatment of yeast cultures at < 2x104 cells/ml with HWS showed complete inhibition of yeast using liquid and agar plates.
Discussion: HWS is effective in eliminating yeast when used undiluted at yeast concentrations < 0.25 -0.5 x105cell/mL. All isolates tested showed similar sensitivity to HWS. Efficacy of HWS is influenced by yeast matrix such as culture media and starting concentration of yeast.
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