Gama João Alves, Zilhão Rita, Dionisio Francisco
cE3c-Centre for Ecology, Evolution and Environmental Changes, Faculdade de Ciências, Universidade de Lisboa, Campo Grande 1749-016, Lisboa, Portugal; Instituto Gulbenkian de Ciência, Oeiras, Portugal.
Departamento de Biologia Vegetal, Faculdade de Ciências, Universidade de Lisboa, Campo Grande 1749-016, Lisboa, Portugal.
Plasmid. 2018 Sep;99:82-88. doi: 10.1016/j.plasmid.2018.09.009. Epub 2018 Sep 19.
Naturally occurring plasmids have medical importance given that they frequently code for virulence or antibiotic resistance. In many cases, plasmids impose a fitness cost to their hosts, meaning that the growth rate of plasmid-bearing cells is lower than that of plasmid-free cells. However, this does not fit with the fact that plasmids are ubiquitous in nature nor that plasmids and their hosts adapt to each other very fast - as has been shown in laboratory evolutionary assays. Even when plasmids are costly, they seem to largely interact in such a way that the cost of two plasmids is lower than the cost of one of them alone. Moreover, it has been argued that transfer rates are too low to compensate for plasmid costs and segregation. Several mechanisms involving interactions between plasmids and other replicons could overcome this limitation, hence contributing to the maintenance of plasmids in bacterial populations. We examine the importance of these mechanisms from a clinical point of view, particularly the spread of antibiotic resistance genes.
天然存在的质粒具有医学重要性，因为它们常常编码毒力或抗生素抗性。在许多情况下，质粒会给宿主带来适应性代价，这意味着携带质粒的细胞的生长速率低于不含质粒的细胞。然而，这与质粒在自然界中无处不在的事实不相符，也与质粒及其宿主能非常快速地相互适应这一情况不相符——实验室进化试验已证明了这一点。即使质粒代价高昂，它们之间的相互作用方式似乎很大程度上使得两个质粒的代价低于其中一个单独存在时的代价。此外，有人认为质粒转移率过低，无法弥补质粒代价和分离损失。涉及质粒与其他复制子之间相互作用的几种机制可以克服这一限制，从而有助于质粒在细菌群体中得以维持。我们从临床角度审视这些机制的重要性，尤其是抗生素抗性基因的传播。
