Bile salt metabolism is not the only factor contributing to Clostridioides (Clostridium) difficile disease severity in the murine model of disease.

Susceptibility of patients to antibiotic-associated C. difficile disease is intimately associated with specific changes to gut microbiome composition. In particular, loss of microbes that modify bile salt acids (BSA) play a central role; primary bile acids stimulate spore germination whilst secondary bile acids limit C. difficile vegetative growth. To determine the relative contribution of bile salt (BS) metabolism on C. difficile disease severity, we treated mice with three combinations of antibiotics prior to infection. Mice given clindamycin alone became colonised but displayed no tissue pathology while severe disease, exemplified by weight loss and inflammatory tissue damage occurred in animals given a combination of 5 antibiotics and clindamycin. Animals given only the 5 antibiotic cocktail showed only transient colonisation and no disease. C. difficile colonisation was associated with a reduction in bacterial diversity, an inability to amplify bile salt hydrolase (BSH) sequences from faecal DNA and a relative increase in primary bile acids (pBA) in caecal lavages from infected mice. Further, the link between BSA modification and the microbiome was confirmed by the isolation of strains of Lactobacillus murinus that modified primary bile acids in vitro, thus preventing C. difficile germination. Interestingly, BSH activity did not correlate with disease severity which appeared linked to alternations in mucin, which may indirectly lead to increased exposure of the epithelial surface to inflammatory signals. These data confirm the role of microbial metabolic activity in protection of the gut and highlights the need for greater understanding the function of bacterial communities in disease prevention.

患者对抗生素相关性艰难梭菌（C. difficile）疾病的易感性，与肠道微生物组（gut microbiome）的组成特异性改变密切相关。尤为关键的是，可修饰胆汁酸（bile salt acids, BSA）的微生物的缺失发挥着核心作用：初级胆汁酸可促进孢子萌发，而次级胆汁酸则会抑制艰难梭菌的营养体生长。为明确胆汁盐（bile salt, BS）代谢在艰难梭菌疾病严重程度中的相对贡献，本研究在感染前为小鼠施加了三种抗生素联合处理方案。仅接受克林霉素处理的小鼠可被艰难梭菌定殖，但未出现组织病理损伤；而接受5种抗生素联合克林霉素处理的小鼠则出现了以体重减轻、炎症性组织损伤为特征的重症疾病。仅接受5种抗生素混合制剂处理的小鼠仅出现暂时性定殖，未发生疾病。艰难梭菌定殖与细菌多样性降低、无法从粪便DNA中扩增出胆汁盐水解酶（bile salt hydrolase, BSH）基因序列，以及感染小鼠盲肠灌洗液中初级胆汁酸（primary bile acids, pBA）相对升高存在关联。此外，本研究通过体外分离可修饰初级胆汁酸的鼠乳杆菌（Lactobacillus murinus）菌株，证实了胆汁酸修饰与肠道微生物组之间的关联，该菌株可抑制艰难梭菌的孢子萌发。值得注意的是，胆汁盐水解酶活性与疾病严重程度并无关联，而疾病严重程度似乎与黏蛋白（mucin）的改变相关，这种改变可能间接导致上皮表面暴露于炎症信号的程度升高。本研究数据证实了微生物代谢活动在肠道保护中的作用，并强调了亟需更深入地理解细菌群落在疾病预防中的功能。