Unité de Recherche en Maladies Infectieuses Tropicales Emergentes (URMITE), CNRS-IRD UMR 6236, Faculté de Médecine, Université de la Méditerranée, Marseille, France.
Clin Microbiol Infect. 2012 Mar;18(3):213-7. doi: 10.1111/j.1469-0691.2012.03781.x.
Virulence factors are thought to be responsible for the virulence capacity of pathogenic bacteria. However, epidemic bacteria were recently found to contain significantly fewer 'virulence factors' than non-epidemic species, and some of the most dangerous epidemic bacteria, such as Mycobacteria spp. and Rickettsia spp., have reduced genomes, and contain hundreds of degraded genes. Epidemic bacteria are actually highly specialized species, characterized by allopatric speciation, that, after adapting to their hosts, attempt to maintain a balance between gene gain and gene loss that favours gene loss, finally leading to genome reduction. Recent comparative genomic studies have demonstrated that the specialization of bacteria to eukaryotic cells is associated with massive gene loss. Furthermore, the 12 deadliest epidemic species for humankind have significantly smaller genomes, with fewer open reading frames, than less dangerous species. Epidemic species mostly lose genes related to metabolic activity, the production of energy, cell motility, and transcription. Epidemic bacteria also possess a damaged recombination and repair system and significantly more toxins than closely related non-pathogenic or non-epidemic species, and more toxin-antitoxin modules. Epidemic bacteria are therefore highly specialized species that are adapted to their hosts and characterized by extensive genome reduction. Except for toxins and toxin-antitoxin modules, which have a direct and measurable effect, other 'virulence factors' are factors associated with fitness in experimental models. Epidemic species are defined by a virulent genomic repertoire including both present and absent genes.
毒力因子被认为是致病菌毒力的原因。然而，最近发现，流行细菌比非流行物种含有明显更少的“毒力因子”，而一些最危险的流行细菌，如分枝杆菌和立克次氏体，基因组已经缩小，并且包含数百个退化的基因。流行细菌实际上是高度专业化的物种，具有异域物种形成的特征，在适应宿主后，它们试图在基因获得和基因丢失之间维持一种有利于基因丢失的平衡，最终导致基因组缩小。最近的比较基因组研究表明，细菌对真核细胞的专业化与大规模基因丢失有关。此外，对人类来说 12 种最致命的流行物种的基因组明显较小，开放阅读框较少，比不那么危险的物种少。流行物种主要失去与代谢活动、能量产生、细胞运动和转录有关的基因。流行细菌还拥有受损的重组和修复系统，并且比密切相关的非致病性或非流行物种拥有更多的毒素和更多的毒素-抗毒素模块。因此，流行细菌是适应宿主的高度专业化物种，其特征是广泛的基因组缩小。除了毒素和毒素-抗毒素模块具有直接和可测量的作用外，其他“毒力因子”是与实验模型中的适应性相关的因素。流行物种的定义是具有包括现有和缺失基因的毒力基因组库。
