Characterization of a New Transposon, Tn 6696, on a bla NDM- 1-Carrying Plasmid From Multidrug-Resistant Enterobacter cloacae ssp. dissolvens in China

Qichao Chen; Yanfeng Lin; Zhonghong Li; Lanfen Lu; Peihan Li; Kaiying Wang; Lang Yang; Hui Ma; Peng Li; Hongbin Song

doi:10.3389/fmicb.2020.525479

Characterization of a New Transposon, Tn 6696, on a bla _NDM- ₁-Carrying Plasmid From Multidrug-Resistant Enterobacter cloacae ssp. dissolvens in China

Front Microbiol. 2020 Sep 15:11:525479. doi: 10.3389/fmicb.2020.525479. eCollection 2020.

Authors

Qichao Chen¹, Yanfeng Lin^{1

2}, Zhonghong Li^{1

3}, Lanfen Lu⁴, Peihan Li^{1

2}, Kaiying Wang^{1

2}, Lang Yang^{1

2}, Hui Ma⁵, Peng Li¹, Hongbin Song¹

Affiliations

¹ Center for Disease Control and Prevention of People's Liberation Army, Beijing, China.
² Academy of Military Medical Sciences, Beijing, China.
³ College of Environmental and Chemical Engineering, Nanchang Hangkong University, Nanchang, China.
⁴ Department of Laboratory Diagnosis, Sun Yat-sen University Affiliated Zhongshan Hospital, Zhongshan, China.
⁵ The Sixth Medical Center of People's Liberation Army General Hospital, Beijing, China.

Abstract

Background: Enterobacter cloacae is an opportunistic pathogen which is responsible for serious nosocomial infections. A gene which plays an important role in resistance to carbapenems is the New Delhi metallo-β-lactamase 1 (NDM-1). Currently, the spread of NDM-1-producing E. cloacae strains is a serious public threat.

Methods: A multidrug-resistant E. cloacae ssp. dissolvens strain CBG15936 was recovered in 2017 in Guangzhou, China. PCR, S1-pulsed-field gel electrophoresis, and Southern blotting were performed to locate the bla _NDM _- ₁ gene. Susceptibility testing and conjugation experiments were also performed. Illumina HiSeq and Nanopore sequencers were used to perform whole-genome sequencing.

Results: Strain CBG15936 belongs to ST932 and is resistant to carbapenems. The bla _NDM- ₁ gene was found on a ∼62-kb plasmid, which has a conjugation frequency of 1.68 × 10^-3 events per donor cell. Genome sequencing and analysis revealed that the NDM-1-carrying IncN1 plasmid contained a new transposon Tn6696, which consists of an intact qnrS1-carrying Tn6292 element, an inverted 8.3-kb Tn3000 remnant, ISkpn19, ΔtnpA, and IS26.

Conclusion: A new transposon, Tn6696, has been detected on a bla _NDM- ₁-carrying plasmid recovered from multidrug-resistant E. cloacae ssp. dissolvens CBG15936 from China. This finding provides a new perspective regarding the potential for bla _NDM- ₁ to undergo horizontal transfer among drug-resistant bacteria.

Keywords: Enterobacter cloacae; Tn6696; blaNDM1; carbapenem resistance; whole genome sequencing.