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Increased Plasmid Copy Number Contributes to the Elevated Carbapenem Resistance in OXA-232-Producing Klebsiella pneumoniae.
Microbial Drug Resistance ( IF 2.6 ) Pub Date : 2020-06-08 , DOI: 10.1089/mdr.2018.0407
Zhen Shen 1 , Haomin Zhang 1 , Qianqian Gao 1 , Juanxiu Qin 1 , Chao Zhang 2 , Junying Zhu 1 , Min Li 1
Affiliation  

A total of 345 unique (one isolate per patient) clinical carbapenem-resistant Klebsiella pneumoniae isolates were recovered in our hospital over the past 3 years (2016–2018), with 325, 14, and 6 isolates carried blaKPC-2, blaNDM-1, and blaOXA-232, respectively. The six OXA-232-Kp isolates were recovered in neurosurgery intensive care unit in 2018. All OXA-232-Kp belonged to ST15, differed by one or two pulsed-field gel electrophoresis (PFGE) bands, and belonged to the same clone. However, three isolates (RJ18-04-6) displayed elevated carbapenem resistance, with imipenem minimum inhibitory concentration (MIC) of 16–32 μg/mL. In contrast, other three isolates (RJ18-01-3) had imipenem MIC of 0.5–1 μg/mL. S1-PFGE revealed two different plasmid profiles and all strains had at least four plasmids. Strain RJ18-01 and RJ18-06 were selected for whole-genome sequencing, and a ColE2-type 6,141 bp blaOXA-232-carrying plasmid was identified. No blaOXA-232 gene was located on chromosome or other plasmids. Furthermore, no β-lactamase resistance gene other than blaCTX-M-15 was identified. Polymerase chain reaction-based sequencing of blaOXA-232-carrying plasmid was performed, and all OXA-232-Kp shared identical blaOXA-232-carrying plasmid sequences. The expression and copy number of blaOXA-232 in RJ18-04-6 were significantly higher than those of other isolates. The hydrolysis activity of nitrocefin and carbapenems were about six-fold higher in RJ18-04-6. Since only one copy of blaOXA-232 gene was spotted on the plasmid, the elevated carbapenem resistance could be attributed to the increased copy number of blaOXA-232-carrying plasmids. OmpK35 porin deficiency was observed in one isolate with decreased carbapenem susceptibility and two isolates with elevated carbapenem resistance, suggesting that OmpK35 deficiency did not significantly alter carbapenem MICs in OXA-232-Kp.

中文翻译:

质粒拷贝数的增加有助于产生OXA-232的肺炎克雷伯菌的碳青霉烯耐药性升高。

在过去的3年中(2016-2018年),我们医院共回收了345株独特的(耐药菌为每株)对碳青霉烯类耐药的临床肺炎克雷伯菌,其中325、14和6株带有bla KPC-2bla NDM -1bla OXA-232, 分别。六个OXA-232-Kp分离株于2018年在神经外科重症监护病房中恢复。所有OXA-232-Kp属于ST15,相差一两个脉冲场凝胶电泳(PFGE)谱带,并且属于同一克隆。但是,三个分离株(RJ18-04-6)表现出较高的碳青霉烯抗性,亚胺培南的最小抑菌浓度(MIC)为16-32μg/ mL。相反,其他三个分离株(RJ18-01-3)的亚胺培南MIC为0.5-1μg/ mL。S1-PFGE揭示了两个不同的质粒图谱,并且所有菌株均具有至少四个质粒。选择菌株RJ18-01和RJ18-06进行全基因组测序,并鉴定出携带ColE2型6,141bp bla OXA-232的质粒。没有bla OXA-232基因位于染色体或其他质粒上。此外,未鉴定到除bla CTX-M-15以外的β-内酰胺酶抗性基因。进行基于bla OXA-232携带质粒的基于聚合酶链反应的测序,并且所有OXA-232-Kp共享相同的bla OXA-232携带质粒的序列。RJ18-04-6中bla OXA-232的表达和拷贝数显着高于其他分离株。在RJ18-04-6中,硝基cefin和碳青霉烯的水解活性高约六倍。由于只有一份bla OXA-232如果在质粒上发现基因,则碳青霉烯抗性的提高可能归因于携带bla OXA-232的质粒的拷贝数增加。在一株碳青霉烯敏感性降低的菌株和两株碳青霉烯耐药性升高的菌株中发现了OmpK35孔蛋白缺乏,这表明OmpK35缺乏并未明显改变OXA-232-Kp中的碳青霉烯MIC。
更新日期:2020-06-08
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