Impediment to growth and yeast-to-hyphae transition in <i>Candida albicans</i> by copper oxide nanoparticles
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The effects of two prominent copper oxide nanoparticles (CuO-NP and Cu<sub>2</sub>O-NP), with the oxidation state of Cu<sup>++</sup> (cupric) and Cu<sup>+</sup> (cuprous), on <i>Candida albicans</i> were evaluated. CuO-NP and Cu<sub>2</sub>O-NP were synthesized and characterized by XRD, FESEM, HR-TEM and Zeta potential. At sub-MIC (50 µg ml<sup>−1</sup>), both cupric and cuprous oxide NPs prevented yeast-to-hyphae switching and wrinkling behaviour in <i>C. albicans</i>. The mechanism for the antifungal action of the two NPs differed; CuO-NP significantly elicited reactive oxygen species, whereas membrane damage was more pronounced with Cu<sub>2</sub>O-NP. Real time PCR analysis revealed that CuO-NP suppressed the morphological switching of yeast-to-hyphae by down-regulating <i>cph1</i>, <i>hst7</i> and <i>ras1</i> and by up-regulation of the negative regulator <i>tup1</i>. In comparison, Cu<sub>2</sub>O-NP resulted in down-regulation of <i>ras1</i> and up-regulation of the negative regulators <i>nrg1</i> and <i>tup1</i>. Between the two NPs, CuO exhibited increased antifungal activity due to its stable oxidation state (Cu<sup>++</sup>) and its smaller dimensions compared with Cu<sub>2</sub>O-NP.
