Objectives: This study aimed to measure the variability in carbapenem susceptibility conferred by different OxaAb variants, characterise the molecular evolution of oxaAb and elucidate the contribution of OxaAb and other possible carbapenem resistance factors in the clinical isolates using WGS and LC-MS/MS. Methods: Disc susceptibility and MIC broth microdilution tests were performed on ten clinical A. baumannii isolates and interpreted according to CLSI guidelines. Imipenem and meropenem MICs were evaluated for all oxaAb variants cloned into susceptible A. baumannii CIP70.10 and increased adeABC efflux pump gene expression BM4547 backgrounds, with and without their natural promoters. Molecular evolution analysis of the oxaAb variants was performed using FastTree and SplitsTree4. Resistance determinants were studied in the clinical isolates using WGS and LC-MS/MS analysis. Results: OxaAb(82), OxaAb(83), OxaAb(107), and OxaAb(110) carrying I129L and L167V substitutions increased carbapenem MICs when transferred into susceptible A. baumannii backgrounds without an upstream IS element. Carbapenem resistance was conferred with the addition of their natural upstream ISAba1 promoter. LC-MS/MS analysis on the original clinical isolates showed no differences in expression levels of proteins commonly associated with carbapenem resistance. Conclusions: ISAba1-driven overexpression of OxaAb variants with substitutions I129L and L167V confers carbapenem resistance with no need for additional resistance mechanisms.

中文翻译：

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鲍曼不动杆菌中固有的OxaAb（OXA-51-like）β-内酰胺酶的碳青霉烯酶活性的变异性

目的： 本研究旨在测量由不同OxaAb赋予变体，表征的分子进化碳代青霉烯的易感性的可变性oxaAb和阐明OxaAb和其他可能的碳青霉烯抗性因子在临床分离株使用WGS和LC-MS / MS的贡献。方法： 对十种临床鲍曼不动杆菌进行了药敏试验和MIC肉汤微稀释试验，并根据CLSI指南进行了解释。对亚胺培南和美罗培南的MIC进行了克隆到易感鲍曼不动杆菌CIP70.10和adeABC增加的所有oxaAb变异体的评估外排泵基因表达BM4547的背景，有或没有其天然启动子。使用FastTree和SplitsTree4对oxaAb变体进行了分子进化分析。使用WGS和LC-MS / MS分析在临床分离株中研究了耐药性决定因素。结果： 当携带I129L和L167V取代的OxaAb（82），OxaAb（83），OxaAb（110）和OxaAb（110）转移到无上游IS元素的易感鲍曼不动杆菌背景中时，碳青霉烯MIC升高。碳青霉烯抗性通过添加其天然上游IS Aba1获得启动子。对原始临床分离株的LC-MS / MS分析显示，通常与碳青霉烯耐药相关的蛋白质表达水平没有差异。结论： IS Aba1驱动的OxaAb变异体的过量表达（具有I129L和L167V取代基）赋予了碳青霉烯耐药性，而无需其他耐药机制。