困難梭狀桿菌是一種會形成芽孢的革蘭氏陽性厭氧菌，廣泛存在於環境中。其芽孢對消毒劑具高度抗性，並可透過糞口途徑進行傳播。困難梭狀桿菌感染的發生主要歸因於腸道菌相失衡及腸道微環境的改變。目前困難梭狀桿菌感染的治療主要依賴抗生素，但約有20%的患者在初次治療後會出現復發。因此，我們積極尋找可用於預防與治療困難梭狀桿菌感染的新型微生物或其代謝產物。腸道菌在調控腸道功能上的效果具有菌株特異性，一些益生菌已被證實能產生具抗菌性的代謝產物，如丁酸與其他短鏈脂肪酸，可抑制病原菌生長。根據我們先前對健康者與感染困難梭狀桿菌病患腸道菌相的分析，發現丁酸產生菌-糞丁酸腸球菌(B. faecihominis)，僅存在於健康組的腸道中，顯示其可能具有抵抗困難梭狀桿菌特性。有趣的是，雖然糞丁酸腸球菌的上清液對困難梭狀桿菌並無抑制作用，但我們從該上清液中純化出奈米級的胞外囊泡(extracellular vesicles, EVs)，並發現這些胞外囊泡能有效抑制困難梭狀桿菌的生長。此外，在以富含毒素A/B的困難梭狀桿菌上清液處理腸道上皮細胞HT-29期間，這些胞外囊泡能提升HT-29細胞的存活率，並促進粒線體生合成。這些結果顯示，糞丁酸腸球菌分泌的代謝產物可來抑制困難梭狀桿菌的生長，或增強宿主抵抗困難梭狀桿菌毒素破壞腸道細胞的能力，從而產生保護作用。最後，動物實驗也顯示糞丁酸腸球菌所分泌的胞外囊泡可緩解困難梭狀桿菌感染小鼠的症狀，包括體重減輕與縮短的結腸長度。本研究提供困難梭狀桿菌感染新的治療選擇。

Clostridioides difficile (C. difficile) is a spore-forming, Gram-positive anaerobic bacterium widely present in the environment. Its spores are resistant to disinfectants and can spread through the fecal-oral route. The mechanism of C. difficile infection is attributed to the dysbiosis of gut microbiota and alterations in the microenvironment. Treatment for C. difficile primarily relies on antibiotics. However, about 20% of patients experience a recurrence after initial treatment. Therefore, we aimed to disclose new therapeutic microorganisms or metabolic products for the prevention and treatment of C. difficile infection. The effectiveness of gut microbiota in regulating intestinal functions is strain-specific. Some probiotics have been shown to produce antimicrobial metabolites, such as butyrate and other short-chain fatty acids (SCFAs), which can inhibit the growth of pathogens. According to our previous analysis of gut microbiota from healthy and C. difficile-infected patients, Butyricicoccus faecihominis, a butyrate-producing Gram-positive bacterium, was detected only in the fecal specimen from the healthy group, suggesting its potential role in colonization resistance against C. difficile. Interestingly, although the supernatant of B. faecihominis did not exhibit inhibitory effects on C. difficile, we purified nanoscale extracellular vesicles (EVs) from this supernatant and found that they effectively inhibit C. difficile. In addition, EVs were able to increase HT-29 cell viability and promote mitochondrial biogenesis during treatment with concentrated C. difficile supernatant, which contains toxin A/B. These findings indicate that metabolites secreted by B. faecihominis exerts protective effects either by directly suppressing the growth of C. difficile or by enhancing the host’s resistance to epithelial injury induced by C. difficile toxins. Finally, animal experiments also showed that B. faecihominis EVs can alleviate symptoms of C. difficile infection in mice, including body weight loss and colon shortening. Therefore, our results suggest that B. faecihominis EVs represent a promising new therapeutic strategy for C. difficile infection.

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