A Novel Transposon, Tn 6518, Mediated Transfer of mcr-3 Variant in ESBL-Producing Aeromonas veronii

Xiaoming Wang; Weishuai Zhai; Shaolin Wang; Zhangqi Shen; Yang Wang; Qidi Zhang

doi:10.2147/IDR.S239865

A Novel Transposon, Tn 6518, Mediated Transfer of mcr-3 Variant in ESBL-Producing Aeromonas veronii

Infect Drug Resist. 2020 Mar 25:13:893-899. doi: 10.2147/IDR.S239865. eCollection 2020.

Authors

Xiaoming Wang^{1

2}, Weishuai Zhai³, Shaolin Wang², Zhangqi Shen², Yang Wang², Qidi Zhang³

Affiliations

¹ MOE Joint International Research Laboratory of Animal Health and Food Safety, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, People's Republic of China.
² Beijing Advanced Innovation Center for Food Nutrition and Human Health, College of Veterinary Medicine, China Agriculture University, Beijing, People's Republic of China.
³ College of Veterinary Medicine, Qingdao Agricultural University, Qingdao, Shandong, People's Republic of China.

Abstract

Purpose: The aim of this study was to determine the prevalence and transmission mechanism of mcr-3 in Aeromonas spp. isolated from chicken cloaca.

Materials and methods: A. veronii w55 was isolated from chicken in 2008. PCR assay was used to detect mcr genes and putative circular intermediate. Susceptibility testing was identified by the microdilution method. WGS was performed to obtain the whole sequence. S1-PFGE and DNA southern hybridization were used to study the location of mcr-3.6.

Results: PCR-based analysis indicated that 1 out of 55 Aeromonas spp. isolates was mcr-3-positive. Whole-genome sequencing revealed that the strain A. veronii w55 belonged to novel sequence type ST514 and had two adjacent chromosomally located mcr variants, mcr-3.6 and mcr-3-like. The mcr-3.6 and mcr-3-like genes showed 93.67% and 82.84% nucleotide sequence identity, respectively, to original mcr-3 from E. coli. A. veronii w55 also exhibited resistance to extended-spectrum β-lactams and was positive for bla _PER-3, and this is the first time to report bla _PER-3 in A. veronii. Genetic environment analysis revealed that the segment of mcr-3.6-mcr-3-like-dgkA was flanked by five insertion sequence elements originated from Aeromonas species, and the structure of ISAs2-ISAhy2-ISAs20-mcr-3.6-mcr-3-like-dgkA-ISAs2 was designated as a novel transposon Tn6518, in which an 8405-bp circular intermediate carrying two mcr-3 variants can be looped out.

Conclusion: This result suggested the mcr-3 variant genes could be disseminated between various Aeromonas species via transposon-mediated transmission.

Keywords: Aeromonas veronii; Tn6158; mcr-3.6.

Grants and funding

This work was supported in part by the grants from the National Key Research and Development Program of China (2016YFD0501304 and 2018YFD0500300), National Natural Science Foundation of China (81661138002), and Qingdao Science and Technology Project (No. 17-3-3-69-nsh).