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.

中文翻译：

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质粒与染色体和其他质粒相互作用对抗生素抗性传播的影响。

由于天然存在的质粒经常编码毒力或抗生素抗性，因此它们具有医学重要性。在许多情况下，质粒对其宿主施加适应性成本，这意味着带有质粒的细胞的生长速率低于不含质粒的细胞的生长速率。但是，这不符合这样的事实，即质粒本质上无处不在，或者质粒及其宿主之间的适应能力非常快，正如实验室进化分析所表明的那样。即使当质粒很昂贵时，它们似乎也以两种质粒的成本低于单独一种质粒的成本的方式相互作用。而且，已经有人提出转移速率太低而不能补偿质粒的成本和分离。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，因此有助于细菌种群中质粒的维持。我们从临床角度检查这些机制的重要性，尤其是抗生素抗性基因的传播。