探討剔除白色念珠菌 CaCDR3、 CaHGT1 及 CaHGT7 對白色念珠菌型態變化及藥物感受性之影響

Abstract

白色念珠菌為人體中伺機性的病原，而其致病力與其型態轉變相關，當白色念珠菌無法在酵母菌型及菌絲型態間轉換時，會降低或失去致病能力。 然而，葡萄糖被認為與菌絲的生成有相關性，本篇研究之基因 CaHGT1 及 CaHGT7 即與葡萄糖的傳送有關，因而被認為與菌絲的生成有關。先前研究也發現菌絲生成與抗藥性有一定的關連，因此由文獻中發現基因 CaCDR1 及 CaCDR2 的過表現會增強菌株對 azole 類藥物的抗藥性。本篇的 CaCDR3 因其序列相似度與 CaCDR1 和 CaCDR2 極高，推測可能與抗藥性現象有關聯。而本研究之目的即在探討此三基因之生理功能是否與型態轉換或抗藥性有直接關係。 本篇研究利用 SAT1 flipper cassette 分別建構出白色念珠菌 CaCDR3、CaHGT1 及 CaHGT7 的雙套基因剔除株，並將建構完成的菌株做型態以及藥物感受性的測試。而結果中，對於型態所做的芽管生成、菌絲生成及侵犯力的實驗，此三基因之剔除菌株與野生株並無明顯不同；在針對藥物 fluzonazole、miconazole 及 amphotericin B 的感受性測試中，其結果也並未發現明顯差異。因此，由結果推測此三基因在測試的條件下，對於白色念珠菌之型態轉變及藥物感受性並非主要調控之基因。

Candida albicans is a major opportunistic pathogen in human. Furthermore, the pathogenicity of C. albicans is related to their morphogenesis, the ability to switch between yeast form and hyphal form. The presence of glucose triggers C.albicans yeast-to-hyphal transition, a vital determinant of virulence. Two genes, CaHGT1 and CaHGT7, members of HGT family (High-affinity Glucose Transporter), may be linked to the formation of filamentous growth. Furthermore, it may also be linked to the drug resistance phenomenon in C. albicans, since previous researches have shown an association between filamentous growth and drug resistance. C. albicans can cause infections in immunocompromised individuals. Azole derivatives are often used for clinical treatments, but the resistance to this class of drugs is becoming common. Two genes, CaCDR1 and CaCDR2, are known to increase the resistance when overexpressed. Orf19.1313 (CaCDR3) possesses high level of homology to Cdr1p and Cdr2p. It is also considered to be potential of drug resistance gene of C. albicans. In this study, I use SAT1 flipper cassette containing a drug selection marker to construct null mutations of CaCDR3, CaHGT1 and CaHGT7 to study the effects on morphology and drug resistance of homologous strain to understand the physiological functions of these genes in C.albicans. The results indicated that CaCDR3, CaHGT1 and CaHGT7 null mutants did not have significant difference than the wild-type on the morphogenesis and drug susceptibilities of C. albicans.