Antifungal activity of some Sternbergia taxa: effects on germ tube and biofilm formation

Natural products are rapidly becoming the primary sources of novel antimicrobial agents, as resistance to existing antimicrobial agents is increasing. Apart from determining the antimicrobial activity of natural products, it is also important to understand their effects on the virulence factors of microorganisms. This study aimed to determine the antimicrobial activity of Sternbergia species prevalent in Turkey and investigate their role in the inhibition of germination tube and biofilm formation, both of which are known to be important virulence factors of Candida albicans. The antimicrobial activities of the plant extracts were evaluated using bore-plate and broth microdilution method. The extracts’ capacity to inhibit the formation of the germ-tube was also evaluated. The findings of our study revealed that Sternbergia lutea, Sternbergia vernalis possessed antimicrobial activities, with MIC values ranging between 0.048 mg/mL and 0.39 mg/mL. The highest antimicrobial activity was observed against Candida dubliniensis (0.048 mg/mL). While evaluating the inhibition of fungal germination activities, S. vernalis extract (at a concentration of 0.09 mg/mL) was found to be the most effective against C. albicans ATCC 90028 strain. The results also indicated that S. vernalis extracts at sub-MIC levels inhibited germ tube formation and modulated the tail-length of germinated cells, both of which are important virulence factors of C. albicans. Furthermore, the inhibition of biofilm-formation was also investigated, and it was found that two Sternbergia spp. extracts at or below MIC levels inhibited biofilm formation.随着现有抗菌药物的耐药性持续攀升，天然产物正迅速成为新型抗菌剂的核心来源。除评估天然产物的抗菌活性外，阐明其对微生物毒力因子的影响同样至关重要。本研究旨在明确土耳其本土分布的斯腾伯格百合属（Sternbergia）植物的抗菌活性，并探究其对真菌芽管与生物被膜形成的抑制作用——二者均为白色念珠菌（Candida albicans）的关键毒力因子。本研究采用打孔平板法与肉汤微量稀释法评估了植物提取物的抗菌活性，同时测定了提取物抑制芽管形成的能力。研究结果显示，黄花斯腾伯格百合（Sternbergia lutea）与春斯腾伯格百合（Sternbergia vernalis）具有抗菌活性，其最低抑菌浓度（MIC，Minimum Inhibitory Concentration）范围为0.048 mg/mL至0.39 mg/mL，其中对都柏林念珠菌（Candida dubliniensis）的抗菌活性最强，MIC值达0.048 mg/mL。在评估真菌芽殖抑制活性时，浓度为0.09 mg/mL的春斯腾伯格百合提取物对白色念珠菌ATCC 90028菌株的抑制效果最佳。研究结果同时表明，亚最低抑菌浓度（sub-MIC）下的春斯腾伯格百合提取物可抑制芽管形成，并调节萌发细胞的尾部长度——这二者均为白色念珠菌的关键毒力因子。此外，本研究还探究了提取物对生物被膜形成的抑制作用，结果显示两种斯腾伯格百合属植物提取物在MIC值及以下浓度时均可抑制生物被膜的形成。