Anticandidal Potential of Stem Bark Extract from Schima superba and the Identification of Its Major Anticandidal Compound

Plant-derived extracts are a promising source of new drugs. Schima superba is traditionally used in China for heat clearing, detoxification, and treatment of furuncles. In this study, the anticandidal properties and mechanism of action of S. superba (SSE) were explored using a stem bark extract. SSE possessed high polyphenol and saponin contents of 256.6 ± 5.1 and 357.8 ± 31.5 µg/mg, respectively. A clear inhibition zone was observed for C. albicans growth through the disc diffusion method and the 50% inhibition of C. albicans by SSE was 415.2 µg/mL. Transcriptomic analysis in C. albicans treated with different doses of SSE was conducted through RNA-seq. Average values of 6068 genes and 20,842,500 clean reads were identified from each sample. Among these samples, 1680 and 1956 genes were differentially expressed genes (DEGs) from the SSE treatments of 0.2 and 0.4 mg/mL, respectively. C. albicans growth was inhibited by the changes in gene expression associated with the cell wall and membrane composition including the regulation of chitin degradation and ergosterol biosynthesis. This result could be reflected in the irregularly wrinkled morphology of the ruptured cell as revealed through SEM analysis. ESI-MS and NMR analyses revealed that the major compound purified from SSE was sasanquasaponin III and the 50% inhibition of C. albicans was 93.1 µg/mL. In summary, the traditional Chinese medicine S. superba can be applied as an anticandidal agent in complementary and alternative medicine.