Recent studies have shown that zebrafish can be used as an infectious disease model host for various pathogens, which are known to associate with either aquatic vertebrate or mammalian pathogenesis. Many human diseases caused by gram-positive /negative bacteria or viruses have been studied successfully in adult or embryonic zebrafish. However, to our knowledge, zebrafish has never been used to study mammal-associated fungal pathogens to date. In this study, we demonstrated that C. albicans, an opportunistic human pathogen, could infect and colonize in adult zebrafish by intra-peritoneal injection. The survival rate assay showed that wild type C. albicans can infect and kill zebrafish in a dose-dependent manner, and the fatality was not caused by endotoxic shock. Moreover, the result of colony-formation assay indicated that the quantity of C. albicans we injected remains consistent. C. albicans could successfully colonize and proliferate within the zebrafish gut. Importantly, using histology analysis-PAS staining and HLC54 (a hyphae-deficit mutant of C. albicans), we found the distinctive yeast-to-hyphae transition of C. albicans, a virulence trait of the pathogen, plays a key role in zebrafish mortality. By RT-qPCR, we also detected specific inflammatory genes responses included up-regulation of IL-1b□□□TNFa and down-regulation of iNOS during C. albicans infection in zebrafish. Furthermore, by successful infection of embryonic zebrafish, we can take advantage of its transparency trait to study host-pathogen interactions in vivo. Taken together, the cost effective zebrafish can be used as an alternative animal model, which is also more manageable than the traditional mouse model, to study C. albicans infection.

現今許多研究報告指出，科學家們可以利用斑馬魚作為宿主研究許多常見的感染性疾病。已經被報導過的研究包括水生生物的致病菌和哺乳動物的致病菌所引起的感染性疾病。針對許多會在人體造成疾病的葛蘭氏陰性菌、葛蘭氏陽性菌或病毒，科學家們也已成功的利用胚胎時期斑馬魚或成魚來進行相關致病機轉的研究。然而直至目前為止，利用斑馬魚來研究人類感染性真菌的平台尚未被建立。在本篇研究中，我們利用腹腔注射的方式，證實白色念珠菌可以感染成年斑馬魚並且在魚體內存活。透過存活率實驗，我們發現白色念珠菌可以透過非內毒素休克致死的方式感染並殺死斑馬魚，且死亡率與注入魚體的白色念珠菌數量成正相關。利用組織切片與過碘酸希夫染色，我們觀察到白色念珠菌的一個致病因子 -- yeast to hyphae transition，會在魚體內發生。藉由在實驗室培養環境下不會生長菌絲的突變白色念珠菌-HLC54，我們發現白色念珠菌的yeast to hyphae transition特性可能是造成被感染的斑馬魚死亡之重要因素。而一些在感染初期很重要的促發炎細胞素，例如介白素1□、腫瘤壞死因子□，和誘導性一氧化氮合成酶，也可藉由即時定量反轉錄聚合酶鏈鎖反應偵測到在其在魚體感染時期的不同表現量。除了利用成魚來進行感染實驗，我們也成功感染胚胎時期的斑馬魚，並利用胚胎時期斑馬魚體透明的特性，直接觀察與病菌在宿主活體內的生長過程。因此，本篇研究建立斑馬魚可作為白色念珠菌宿主物種的新選擇，之於傳統的老鼠宿主模式，使用斑馬魚可以達到有效降低實驗成本、操作方便、繁殖大量且快速的優點，預期未來在白色念珠菌感染性疾病研究上有更大的應用與發展空間。

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