Centre of Infectious Diseases, West China Hospital, Sichuan University, Chengdu, China; Division of Infectious Diseases, State Key Laboratory of Biotherapy, Chengdu, China; Department of Infectious Diseases, The Affiliated Hospital, Guizhou Medical University, Guiyang, China.
Centre for Pathogen Research, West China Hospital, Sichuan University, Chengdu, China; Division of Infectious Diseases, State Key Laboratory of Biotherapy, Chengdu, China.
Int J Antimicrob Agents. 2023 Nov;62(5):106985. doi: 10.1016/j.ijantimicag.2023.106985. Epub 2023 Sep 27.
Acquired β-lactamase-encoding genes are typically carried by large plasmids in Gram-negative bacteria, which also commonly carry multi-copy small plasmids. This study found that mobile genetic elements carrying antimicrobial resistance genes are capable of hijacking small plasmids. This study focused on aztreonam-avibactam (ATM-AVI) as this combination can be used to effectively counter almost all β-lactamases produced by bacteria, and has been recommended against carbapenem-resistant Enterobacterales. A clinical strain (085003) of carbapenem-resistant Escherichia coli was investigated, and mutants (085003R32 and 085003R512) able to grow under 32/4 and 512/4 mg/L of ATM-AVI were obtained as representatives of low- and high-level resistance, respectively, by induction. Comparative genomics showed that 085003R32 and 085003R512 had a single nucleotide mutation of β-lactamase gene bla, encoding a novel CMY with a Thr319Ile substitution, assigned 'CMY-2R'. Cloning and enzyme kinetics were used to verify that CMY-2R conferred ATM-AVI resistance by compromising binding of AVI and subsequent protection of ATM. Mechanisms for the discrepant resistance between 085003R32 and 085003R512 were investigated. Three tandem copies of bla were identified on a self-transmissible IncP1 plasmid of 085003R32 due to IS1294 misrecognizing its end terIS and rolling-circle replication. 085003R512 had only a single copy of bla on the IncP1 plasmid, but possessed anther bla on an already present 4-kb small plasmid. IS1294-mediated mobilization on to this multi-copy small plasmid increased the copy number of bla significantly, rendering higher resistance. This study shows that bacteria can employ multiple approaches to accommodate selection pressures imposed by exposure to varied concentrations of antimicrobial agents.
获得性β-内酰胺酶编码基因通常由革兰氏阴性菌中的大型质粒携带，这些细菌还通常携带多拷贝的小型质粒。本研究发现，携带抗微生物药物耐药基因的可移动遗传元件能够劫持小型质粒。本研究重点关注氨曲南-阿维巴坦（ATM-AVI），因为这种组合可有效对抗细菌产生的几乎所有β-内酰胺酶，并且已被推荐用于治疗耐碳青霉烯类肠杆菌科细菌。本研究调查了一株耐碳青霉烯类大肠埃希菌（085003）的临床分离株，通过诱导获得了能够在 32/4 和 512/4mg/L ATM-AVI 下生长的突变株（085003R32 和 085003R512），分别代表低水平和高水平耐药。比较基因组学表明，085003R32 和 085003R512 的β-内酰胺酶基因 bla 发生了单个核苷酸突变，编码一种新的 CMY，其 Thr319Ile 取代，被指定为“CMY-2R”。通过克隆和酶动力学验证，CMY-2R 通过破坏 AVI 的结合和随后对 ATM 的保护，赋予 ATM-AVI 耐药性。还研究了 085003R32 和 085003R512 之间耐药性差异的机制。由于 IS1294 错误识别其末端 terIS 并进行滚环复制，导致 085003R32 上的 bla 位于一个可自我转移的 IncP1 质粒上，有三个串联拷贝。085003R512 在 IncP1 质粒上只有 bla 的单个拷贝，但在已经存在的 4kb 小型质粒上还有另一个 bla。IS1294 介导的转座到这个多拷贝小型质粒上，显著增加了 bla 的拷贝数，从而提高了耐药性。本研究表明，细菌可以采用多种方法来适应暴露于不同浓度抗微生物药物所带来的选择压力。
