抗微生物光動力治療

Antimicrobial Photodynamic Therapy

抗生素的濫用導致微生物對許多抗生素產生抗藥性，導致治療上的困難，因此發展出更有效處理微生物感染問題的新方法，實在是一件迫切需要的事。目前科學家已經證實利用光動力治療的方法可以殺死微生物。光動力殺菌（photodynamic inactivation）為一有別於傳統抗菌藥物治療微生物感染的方法；光動力殺菌過程中光感物質可迅速地累積在菌體，並經由特定波長的光源激發後，產生單態氧及自由基對微生物細胞進行毒殺，形成不可逆的傷害。光動力殺菌對細菌或真菌具有立即殺菌效果，不同於抗生素的殺菌機轉。目前沒有證據顯示微生物會產生對抗單態氧的機轉而對光動力殺菌產生抗性。聚合物微胞（micelles）與微脂體（liposomes）同樣都具有避免光感物質在水溶液中聚集而改善光動力的效率，而微胞之優點在於除了殺菌效率相同於或更優於微脂體外，成本低廉、容易製備等更顯示其潛力。甲殼素（chitosan）應用在光動力作用上，能夠提升光動力作用抑制細菌或真菌生長的效率。利用紅色之發光二極體光源來激發5-氨基酮戊酸（5-aminolevulinic acid）以應用在疣的光動力治療上，它不但有效，治癒率達九成以上，簡單又不留疤，唯一的缺點是在照光時有輕微至中等程度的痛。因此光動力治療在抗微生物的應用上，已成為光動力醫學領域中的重要的研究領域，不僅能減少抗生素使用，避免抗藥性微生物產生，更能用來治療抗藥性微生物的局部感染。

The rise of multi-drug-resistant bacteria and fungi has led to search for novel antimicrobial therapies to treat infections. Photodynamic inactivation (PDI) is a potential candidate; it uses the combination of a photosensitizer (PS) with visible light to produce reactive oxygen species that lead to cell death. There was no evidence that repeated PDI could induce resistance of the microbes against this treatment. To increase the efficacy of PDI, PS could be encapsulated either in liposomes or micelles to prevent aggregation in aqueous medium. Evidences indicate that PS entrapped in micelle exert similar or better PDI efficacy than that of liposome, which indicates that this formulation may be useful for the treatment of local infections. Our studies also showed that chitosan can potentiate the PDI efficacy against bacteria and yeasts in planktonic cells or biofilms. After PDI application, the addition of chitosan can greatly augment the killing of microbes. Besides, using LED red light, we showed that topical 5-aminolevulinic acid (ALA) photodynamic therapy (PDT) was a effective treatment of verruca vulgaris. It cured the warts mostly on the feet and hands with a complete cure rate more than 90%. The advantages of ALA-PDT were simplicity and leaving no scar, although mild to moderate pain occurred during illumination. In conclusion, antimicrobial PDT has been applied extensively and not only plays an important role in preventing the emergences of multi-drugs-resistant microbes, it also can cure local infections of drug-resistant microbes.