The carbapenem resistance gene bla OXA-23 is disseminated by a conjugative plasmid containing the novel transposon Tn 66
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RESEARCH
The carbapenem resistance gene blaOXA‑23 is disseminated by a conjugative plasmid containing the novel transposon Tn6681 in Acinetobacter johnsonii M19 Gongli Zong1,2,3, Chuanqing Zhong4, Jiafang Fu2,3,5, Yu Zhang4, Peipei Zhang2,3,5, Wenchi Zhang6, Yan Xu1, Guangxiang Cao2,3* and Rongzhen Zhang1*
Abstract Background: Carbapenem resistant Acinetobacter species have caused great difficulties in clinical therapy in the worldwide. Here we describe an Acinetobacter johnsonii M19 with a novel blaOXA-23 containing transposon Tn6681 on the conjugative plasmid pFM-M19 and the ability to transferand carbapenem resistance. Methods: A. johnsonii M19 was isolated under selection with 8 mg/L meropenem from hospital sewage, and the minimum inhibitory concentrations (MICs) for the representative carbapenems imipenem, meropenem and ertapenem were determined. The genome of A. johnsonii M19 was sequenced by PacBio RS II and Illumina HiSeq 4000 platforms. A homologous model of OXA-23 was generated, and molecular docking models with imipenem, meropenem and ertapenem were constructed by Discovery Studio 2.0. Type IV secretion system and conjugation elements were identified by the Pathosystems Resource Integration Center (PATRIC) server and the oriTfinder. Mating experiments were performed to evaluate transfer of OXA-23 to Escherichia coli 25DN. Results: MICs of A. johnsonii M19 for imipenem, meropenem and ertapenem were 128 mg/L, 48 mg/L and 24 mg/L, respectively. Genome sequencing identified plasmid pFM-M19, which harbours the carbapenem resistance gene blaOXA-23 within the novel transposon Tn6681. Molecular docking analysis indicated that the elongated hydrophobic tunnel of OXA-23 provides a hydrophobic environment and that Lys-216, Thr-217, Met-221 and Arg-259 were the conserved amino acids bound to imipenem, meropenem and ertapenem. Furthermore, pFM-M19 could transfer blaOXA-23 to E. coli 25DN by conjugation, resulting in carbapenem-resistant transconjugants. Conclusions: Our investigation showed that A. johnsonii M19 is a source and disseminator of blaOXA-23 and carbapenem resistance. The ability to transfer blaOXA-23 to other species by the conjugative plasmid pFM-M19 raises the risk of spread of carbapenem resistance. Keywords: Acinetobacter johnsonii, Carbapenem resistance, Conjugative plasmid, Novel transposon Tn6681, blaOXA-23
*Correspondence: caozhong0402@163.com; rzzhang@jiangnan.edu.cn 1 Key Laboratory of Industrial Biotechnology of Ministry of Education and School of Biotechnology, Jiangnan University, Wuxi 214122, China 2 Department of Epidemiology, The First Affiliated Hospital of Shandong First Medical University, Jinan 250062, China Full list of author information is available at the end of the article
Introduction Carbapenems are considered to be reliable and effective antibiotic agents against most pathogenic bacteria because of their broad antibacterial spectrum [1] and are used in the treatment of serious nosocomial infections caused by cephalosporin-resistant bacteria [1]. Species of
