Antifungal effects of the flavonoids kaempferol and quercetin: a possible alternative for the control of fungal biofilms

This study aimed to determine the minimum inhibitory concentration (MIC) of kaempferol and quercetin against planktonic and biofilm forms of the <i>Candida parapsilosis</i> complex. Initially, nine <i>C. parapsilosis sensu stricto</i>, nine <i>C. orthopsilosis</i> and nine <i>C. metapsilosis</i> strains were used. Planktonic susceptibility to kaempferol and quercetin was assessed. Growing and mature biofilms were then exposed to the flavonoids at MIC or 10xMIC, respectively, and theywere also analyzed by confocal laser scanning microscopy. The MIC ranges were 32-128 µg ml⁻¹ for kaempferol and 0.5-16 µg ml⁻¹ for quercetin. Kaempferol and quercetin decreased (P C. <i>parapsilosis</i> complex. As for mature biofilms, the metabolic effects of the flavonoids varied, according to the cryptic species, but kaempferol caused an overall reduction in biofilm biomass. Microscopic analyses showed restructuring of biofilms after flavonoid exposure. These results highlight the potential use of these compounds as sustainable resources for the control of fungal biofilms.

本研究旨在测定山奈酚（kaempferol）与槲皮素（quercetin）对浮游态（planktonic）及生物被膜（biofilm）态近平滑念珠菌复合群（Candida parapsilosis complex）的最低抑菌浓度（minimum inhibitory concentration, MIC）。初始实验共纳入9株近平滑念珠菌严格型（C. parapsilosis sensu stricto）、9株邻近平滑念珠菌（C. orthopsilosis）及9株伴近平滑念珠菌（C. metapsilosis）菌株。本研究评估了两种黄酮类化合物（flavonoids）对浮游态菌体的抑菌敏感性。随后分别将处于生长期与成熟期的生物被膜暴露于对应最低抑菌浓度（MIC）或10倍最低抑菌浓度（10×MIC）的受试化合物，并通过激光共聚焦扫描显微镜（confocal laser scanning microscopy）进行分析。结果显示，山奈酚的最低抑菌浓度范围为32~128 μg·mL⁻¹，槲皮素则为0.5~16 μg·mL⁻¹。山奈酚与槲皮素可显著降低近平滑念珠菌复合群浮游态菌体的活性（P < 0.05）。针对成熟期生物被膜，黄酮类化合物的代谢效应因隐秘菌种而异，但山奈酚可整体降低生物被膜的生物量。显微分析结果表明，黄酮类化合物暴露后，生物被膜发生了结构重塑。本研究结果凸显了这类化合物作为可持续资源，用于调控真菌生物被膜的应用潜力。