With a great diversity in gene composition, including multiple putative antibiotic resistance genes, AbaR islands are potential contributors to multidrug resistance in Acinetobacter baumannii. However, the effective contribution of AbaR to antibiotic resistance and bacterial physiology remains elusive. To address this, we sought to accurately remove AbaR islands and restore the integrity of their insertion site. To this end, we devised a versatile scarless genome editing strategy. We performed this genetic modification in two recent A. baumannii clinical strains: the strain AB5075 and the nosocomial strain AYE, which carry AbaR11 and AbaR1 islands of 19.7 kbp and 86.2 kbp, respectively. Antibiotic susceptibilities were then compared between the parental strains and their AbaR-cured derivatives. As anticipated by the predicted function of the open reading frame (ORF) of this island, the antibiotic resistance profiles were identical between the wild type and the AbaR11-cured AB5075 strains. In contrast, AbaR1 carries 25 ORFs, with predicted resistance to several classes of antibiotics, and the AYE AbaR1-cured derivative showed restored susceptibility to multiple classes of antibiotics. Moreover, curing of AbaRs restored high levels of natural transformability. Indeed, most AbaR islands are inserted into the comM gene involved in natural transformation. Our data indicate that AbaR insertion effectively inactivates comM and that the restored comM is functional. Curing of AbaR consistently resulted in highly transformable and therefore easily genetically tractable strains. Emendation of AbaR provides insight into the functional consequences of AbaR acquisition.

中文翻译：

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毫不留情地去除大抗性岛AbaR会导致鲍曼不动杆菌的抗生素敏感性和自然转化性增加。

AbaR岛具有广泛的基因组成，包括多个推定的抗生素抗性基因，是鲍曼不动杆菌多药耐药性的潜在贡献者。但是，AbaR对抗生素抗性和细菌生理的有效贡献仍然难以捉摸。为了解决这个问题，我们试图准确地去除AbaR岛并恢复其插入位点的完整性。为此，我们设计了一种通用的无痕基因组编辑策略。我们在两个最近的鲍曼不动杆菌中进行了这种基因修饰临床菌株：AB5075菌株和医院菌株AYE，分别携带19.7 kbp和86.2 kbp的AbaR11和AbaR1岛。然后在亲本菌株及其经AbaR固化的衍生物之间比较抗生素敏感性。如该岛的开放阅读框（ORF）的预测功能所预期的那样，在野生型和AbaR11固化的AB5075菌株之间，抗生素耐药性特征相同。相比之下，AbaR1携带25个ORF，具有对几种抗生素的预测抗性，而AYE AbaR1固化的衍生物显示出对多种抗生素的敏感性恢复。此外，AbaRs的固化恢复了高水平的自然可转化性。实际上，大多数AbaR岛都插入了comM基因参与自然转化。我们的数据表明AbaR插入有效地使comM失活，并且恢复的comM起作用。AbaR的固化始终产生高度可转化的菌株，因此易于遗传治疗。AbaR的修订版可以深入了解AbaR收购的功能后果。