Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA.
Microbiol Mol Biol Rev. 2013 Jun;77(2):208-33. doi: 10.1128/MMBR.00062-12.
In both humans and animals, Clostridium perfringens is an important cause of histotoxic infections and diseases originating in the intestines, such as enteritis and enterotoxemia. The virulence of this Gram-positive, anaerobic bacterium is heavily dependent upon its prolific toxin-producing ability. Many of the ∼16 toxins produced by C. perfringens are encoded by large plasmids that range in size from ∼45 kb to ∼140 kb. These plasmid-encoded toxins are often closely associated with mobile elements. A C. perfringens strain can carry up to three different toxin plasmids, with a single plasmid carrying up to three distinct toxin genes. Molecular Koch's postulate analyses have established the importance of several plasmid-encoded toxins when C. perfringens disease strains cause enteritis or enterotoxemias. Many toxin plasmids are closely related, suggesting a common evolutionary origin. In particular, most toxin plasmids and some antibiotic resistance plasmids of C. perfringens share an ∼35-kb region containing a Tn916-related conjugation locus named tcp (transfer of clostridial plasmids). This tcp locus can mediate highly efficient conjugative transfer of these toxin or resistance plasmids. For example, conjugative transfer of a toxin plasmid from an infecting strain to C. perfringens normal intestinal flora strains may help to amplify and prolong an infection. Therefore, the presence of toxin genes on conjugative plasmids, particularly in association with insertion sequences that may mobilize these toxin genes, likely provides C. perfringens with considerable virulence plasticity and adaptability when it causes diseases originating in the gastrointestinal tract.
在人类和动物中，产气荚膜梭菌是一种重要的组织毒性感染和起源于肠道的疾病的原因，如肠炎和肠毒血症。这种革兰氏阳性、厌氧细菌的毒力在很大程度上取决于其丰富的产毒能力。产气荚膜梭菌产生的约 16 种毒素中有许多是由大小在 45kb 到 140kb 之间的大型质粒编码的。这些质粒编码的毒素通常与移动元件密切相关。产气荚膜梭菌菌株可以携带多达三种不同的毒素质粒，单个质粒可以携带多达三种不同的毒素基因。分子科赫假设分析已经确定了几种质粒编码的毒素在产气荚膜梭菌疾病菌株引起肠炎或肠毒血症时的重要性。许多毒素质粒密切相关，表明它们有共同的进化起源。特别是，大多数毒素质粒和一些产气荚膜梭菌的抗生素抗性质粒都有一个大约 35kb 的区域，其中包含一个名为 tcp（clostridial plasmids transfer，梭状芽孢杆菌质粒转移）的 Tn916 相关的转导基因座。这个 tcp 基因座可以介导这些毒素或抗性质粒的高效转导。例如，从感染菌株向产气荚膜梭菌正常肠道菌群菌株的毒素质粒的共轭转移可能有助于放大和延长感染。因此，在与可能移动这些毒素基因的插入序列相关的共轭质粒上存在毒素基因，可能为产气荚膜梭菌在引起胃肠道疾病时提供了相当大的毒力可塑性和适应性。
