The vast majority of Escherichia coli and Klebsiella pneumoniae isolated from human clinical extra-intestinal infections are now multi-drug resistant (MDR). Extended Spectrum Beta Lactamase (ESBL) carriage in clinical isolates of these bacteria is now commonplace, and carriage of carbapenemases is continuing to increase. MDR is primarily concentrated in a small number of globally disseminated clones, which generally differ between ESBL and carbapenemase carrying-clones in E. coli, but seem to converge in K. pneumoniae. In both species MDR is mediated by acquisition and maintenance of MDR plasmids. The plasmids associated with ESBL and carbapenemases also differ, and when both resistances are present in the same strain they are generally on distinct plasmids. Recent research is attempting to provide clues as to why some lineages appear better suited to acquisition and maintenance of these plasmids without a fitness cost. Central to this is the appearance of adaptive mutations in intergenic regions, and selection on genes involved in anaerobic metabolism, hinting at a process whereby these clones can outcompete commensal strains of the same species to initiate long-term intestinal colonization.

中文翻译：

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多重耐药性大肠杆菌和肺炎克雷伯菌的进化和传播：克隆和质粒的复杂性。

从人临床肠外感染中分离出的绝大多数大肠杆菌和肺炎克雷伯菌现具有多重耐药性（MDR）。这些细菌的临床分离物中的超广谱β内酰胺酶（ESBL）携带现在很普遍，碳青霉烯酶的携带也在继续增加。MDR主要集中在少数在全球范围内传播的克隆中，这些克隆通常在大肠杆菌中的ESBL和碳青霉烯酶携带克隆之间有所不同，但似乎在肺炎克雷伯氏菌中趋同。在两种物种中，MDR都是通过MDR质粒的获取和维持来介导的。与ESBL和碳青霉烯酶相关的质粒也不同，并且当两种抗性同时存在于同一菌株中时，它们通常位于不同的质粒上。最近的研究试图提供线索，说明为什么有些谱系看起来更适合于在不花费健身费用的情况下获取和维持这些质粒。关键在于基因间区域的适应性突变的出现，以及对厌氧代谢相关基因的选择，这暗示了这些克隆可以胜过相同物种的共生菌株以启动长期肠道定植的过程。