Clostridia Research Group, Centre for Biomolecular Sciences, School of Molecular Medical Sciences, Nottingham Digestive Diseases Centre, NIHR Biomedical Research Unit, University of Nottingham, Nottingham NG7 2RD, UK.
Nature. 2010 Oct 7;467(7316):711-3. doi: 10.1038/nature09397. Epub 2010 Sep 15.
Clostridium difficile infection is the leading cause of healthcare-associated diarrhoea in Europe and North America. During infection, C. difficile produces two key virulence determinants, toxin A and toxin B. Experiments with purified toxins have indicated that toxin A alone is able to evoke the symptoms of C. difficile infection, but toxin B is unable to do so unless it is mixed with toxin A or there is prior damage to the gut mucosa. However, a recent study indicated that toxin B is essential for C. difficile virulence and that a strain producing toxin A alone was avirulent. This creates a paradox over the individual importance of toxin A and toxin B. Here we show that isogenic mutants of C. difficile producing either toxin A or toxin B alone can cause fulminant disease in the hamster model of infection. By using a gene knockout system to inactivate the toxin genes permanently, we found that C. difficile producing either one or both toxins showed cytotoxic activity in vitro that translated directly into virulence in vivo. Furthermore, by constructing the first ever double-mutant strain of C. difficile, in which both toxin genes were inactivated, we were able to completely attenuate virulence. Our findings re-establish the importance of both toxin A and toxin B and highlight the need to continue to consider both toxins in the development of diagnostic tests and effective countermeasures against C. difficile.
艰难梭菌感染是欧洲和北美的主要医疗保健相关腹泻的原因。在感染过程中，艰难梭菌产生两种关键的毒力决定因素，毒素 A 和毒素 B。使用纯化毒素的实验表明，单独的毒素 A 就能够引起艰难梭菌感染的症状，但毒素 B 不能引起，除非它与毒素 A 混合，或者肠道黏膜已经受到先前的损伤。然而，最近的一项研究表明，毒素 B 对艰难梭菌的毒力是必不可少的，而单独产生毒素 A 的菌株则没有毒力。这就产生了毒素 A 和毒素 B 各自重要性的悖论。在这里，我们表明，单独产生毒素 A 或毒素 B 的艰难梭菌的同源突变株能够在感染的仓鼠模型中引起暴发性疾病。通过使用基因敲除系统永久失活毒素基因，我们发现单独产生一种或两种毒素的艰难梭菌在体外具有细胞毒性活性，这直接转化为体内的毒力。此外，通过构建艰难梭菌的第一个双突变株，其中两个毒素基因都被失活，我们能够完全减弱毒力。我们的研究结果重新确立了毒素 A 和毒素 B 的重要性，并强调需要继续在诊断测试和针对艰难梭菌的有效对策的开发中考虑这两种毒素。
