Infection and Drug Resistance (Mar 2020)
A Novel Transposon, Tn6518, Mediated Transfer of mcr-3 Variant in ESBL-Producing Aeromonas veronii
Abstract
Xiaoming Wang,1,2 Weishuai Zhai,3 Shaolin Wang,2 Zhangqi Shen,2 Yang Wang,2 Qidi Zhang3 1MOE Joint International Research Laboratory of Animal Health and Food Safety, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, People’s Republic of China; 2Beijing Advanced Innovation Center for Food Nutrition and Human Health, College of Veterinary Medicine, China Agriculture University, Beijing, People’s Republic of China; 3College of Veterinary Medicine, Qingdao Agricultural University, Qingdao, Shandong, People’s Republic of ChinaCorrespondence: Qidi Zhang No. 700 Changcheng Road, Chengyang District, Qingdao City, Shandong Province 266109, People’s Republic of ChinaEmail [email protected]: 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 blaPER-3, and this is the first time to report blaPER-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 Tn 6518, 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: mcr-3.6, Tn 6158, Aeromonas veronii
