Genomic and transcriptomic study of high potential virulence strains of Clostridium difficile. Clostridioides difficile T23

Clostridium difficile-associated diarrhoea (CDAD) is currently the most frequently occurring nosocomial infection in many European hospitals. Clostridium difficile induces severe diarrhoea in patients with compromised normal gut flora due to antibiotic usage and/or underlying disease conditions. Clinical severity ranges from mild, self-limiting diarrhoea to the potentially fatal pseudomembranous colitis (PMC). The incidence and severity of CDAD has shown a dramatic increase since 2003. It can be partially explained by the emergence of a highly virulent type (ribotype 027) throughout North America and Europe. The two large toxins, toxin A and B, produced by the pathogenic Clostridium difficile strains have been recognized as the main virulence factors. But studies of genotypes with increased virulence have revealed that in addition to host factors (immunity…), other bacterial virulence factors have to be involved. Most of the current studies on increased virulence have currently concentrated to type 027. However, we assume that other Clostridium difficile strains which are at present less numerous and only occasionally associated with severe cases and outbreaks, might have an increased virulence potential and could represent the future epidemic types. The objectives of this project are to use genomic approaches to define Clostridium difficile groups with increased virulence potential and subsequently analyze their genomic characteristics in terms of the presence of known and new virulence factors, regulation of their expression and genomic heterogeneity. By using genomic and transcriptomic approaches, we will compare genomic differences and differences in gene expression among the genotypes associated with increased virulence and control groups from asymptomatic carriers or mild cases. Genes potentially associated with hypervirulence characters identified will be tested further for their role in the pathogenesis process and/or in the interaction with the host by constructing knockout mutants and challenged in the animal models.

艰难梭菌相关性腹泻（Clostridium difficile-associated diarrhoea, CDAD）目前是欧洲众多医院中最为高发的医院获得性感染。艰难梭菌（Clostridium difficile）可导致因抗生素使用及/或基础疾病而出现正常肠道菌群受损的患者发生重症腹泻。其临床严重程度跨度较大，从轻度自限性腹泻，直至潜在致命的假膜性结肠炎（pseudomembranous colitis, PMC）。自2003年以来，CDAD的发病率与严重程度均出现显著攀升，这一现象可部分归因于高毒力核糖体型027（ribotype 027）在北美与欧洲的广泛出现。致病性艰难梭菌菌株所产生的两大毒素——毒素A与毒素B，已被确认为主要毒力因子。但针对毒力增强菌株的基因型研究表明，除宿主相关因素（如免疫力……）外，还需其他细菌毒力因子参与致病过程。当前多数关于毒力增强的研究均集中于核糖体型027。然而我们推测，目前数量较少、仅偶尔与重症病例及暴发疫情相关的其他艰难梭菌菌株，或许具备更高的毒力潜力，并可能成为未来的流行菌株。本项目的研究目标为：采用基因组学方法，明确具备高毒力潜力的艰难梭菌菌群；随后从已知与新型毒力因子的存在情况、其表达调控及基因组异质性等维度，分析这些菌株的基因组特征。我们将通过基因组学与转录组学方法，对比毒力增强相关基因型菌株与对照组（无症状携带者或轻症病例菌株）之间的基因组差异及基因表达差异。鉴定出的与高毒力特性相关的候选基因，将通过构建敲除突变体（knockout mutants）并在动物模型（animal models）中开展攻毒实验，进一步验证其在致病过程及/或与宿主互作中的作用。