Background The combination aztreonam/avibactam is currently under Phase 3 trials for the treatment of serious infections caused by Gram-negative bacteria including those with MBLs. Objectives To investigate the resistance mechanisms in Enterobacterales exhibiting aztreonam/avibactam MICs of ≥4 mg/L. Methods Among 8787 Enterobacterales, 17 (0.2%) isolates exhibited an aztreonam/avibactam MIC of ≥4 mg/L. Isolates were sequenced and screened for β-lactamases. Sequences of porins, penicillin-binding protein 3 (PBP3) and expression levels of AmpC and AcrA were evaluated. Results Eleven (11/4154 isolates; 0.26%) Escherichia coli, three (3/1981; 0.15%) Klebsiella pneumoniae and three (3/628; 0.5%) Enterobacter cloacae were identified. All E. coli showed either an ‘YRIK’ or ‘YRIN’ insertion in PBP3. In general, these isolates carried blaCMY and/or blaCTX-M variants, except for one isolate from Korea that also produced NDM-5 and one isolate from Turkey that produced OXA-48. Two DHA-1-producing K. pneumoniae overexpressed acrA and had a premature stop codon in either OmpK35 or OmpK36, whereas a third K. pneumoniae carried blaPER-2 and had a premature stop codon in OmpK35. All three E. cloacae expressed AmpC at levels ≥570-fold, but sequence analysis did not reveal known amino acid alterations associated with decreased avibactam binding or increased hydrolysis of β-lactams. Minor amino acid polymorphisms within OmpC, OmpF and PBP3 were noted among the E. cloacae. Conclusions A small number of isolates (0.2%) met the inclusion criteria. E. coli showed altered PBP3 as the most relevant resistance mechanism, whereas K. pneumoniae had multiple resistance mechanisms. Further investigations are needed to clarify resistance in E. cloacae.

中文翻译：

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2019 年在欧洲、亚洲和拉丁美洲收集的肠杆菌临床分离株中氨曲南/阿维巴坦活性敏感性降低的机制研究

背景 氨曲南/阿维巴坦联合用药目前处于 3 期试验阶段，用于治疗由革兰氏阴性菌引起的严重感染，包括 MBLs。目的 研究氨曲南/阿维巴坦 MIC ≥ 4 mg/L 的肠杆菌的耐药机制。方法 在 8787 株肠杆菌中，17 株（0.2%）分离株的氨曲南/阿维巴坦 MIC ≥4 mg/L。对分离物进行测序并筛选β-内酰胺酶。评估了孔蛋白、青霉素结合蛋白 3 (PBP3) 的序列以及 AmpC 和 AcrA 的表达水平。结果 鉴定出 11 株（11/4154 株；0.26%）大肠杆菌、3 株（3/1981 年；0.15%）肺炎克雷伯菌和 3 株（3/628；0.5%）阴沟肠杆菌。所有大肠杆菌都在 PBP3 中显示了“YRIK”或“YRIN”插入。一般来说，这些分离株携带 blaCMY 和/或 blaCTX-M 变体，除了一种来自韩国的分离株也产生 NDM-5 和一种来自土耳其的分离株产生 OXA-48。两个产生 DHA-1 的肺炎克雷伯菌过表达 acrA 并在 OmpK35 或 OmpK36 中具有过早终止密码子，而第三个肺炎克雷伯菌携带 blaPER-2 并在 OmpK35 中具有过早终止密码子。所有三种阴沟肠杆菌均以 ≥570 倍的水平表达 AmpC，但序列分析未揭示与 avibactam 结合减少或 β-内酰胺水解增加相关的已知氨基酸改变。在阴沟肠杆菌中发现了 OmpC、OmpF 和 PBP3 内的次要氨基酸多态性。结论 少数分离株（0.2%）符合纳入标准。大肠杆菌显示改变的 PBP3 是最相关的抗性机制，而 K. 肺炎链球菌具有多种耐药机制。需要进一步的研究来阐明阴沟肠杆菌的耐药性。