Potential dissemination of IncHI2/IncHI2A plasmids carrying mcr-9.4 complex transposon in chicken-derived Enterobacter hormaechei

Microbiology Spectrum

卷:14

Research Article

Panpan Liu^1,2  Mengke Ru³  Baocheng Hao³  Ling Wang³  Shengyi Wang³  Haipeng Cheng⁴  Dongan Cui^1,2,3 

[1] Beijing Kangmu Biological Technology Co., LTD, Beijng, China

[2] Gansu Province Research Center for Basic Disciplines of Pathogen Biology, Lanzhou, China

[3] State Key Laboratory of Animal Disease Control and Prevention, College of Veterinary Medicine, Lanzhou Veterinary Research Institute, Lanzhou University, Chinese Academy of Agricultural Sciences, Lanzhou, China

[4] Lanzhou Institute of Husbandry and Pharmaceutical Sciences, Chinese Academy of Agriculture Sciences, Lanzhou, China

关键词: antimicrobial resistance;    colistin;    Enterobacter cloacae complex;    mcr-9;   

DOI  :  10.1128/spectrum.01979-25

 received in 2025-07-02, accepted in 2025-11-24,  发布年份 2026

来源: American Society for Microbiology

【 摘 要 】

ABSTRACTThe escalating global prevalence of antimicrobial resistance(AMR) represents a critical public health challenge, particularly concerning the compromised efficacy of polymyxins—essential therapeutic agents against carbapenem-resistant Gram-negative pathogens. This crisis is exacerbated by the plasmid-mediated horizontal gene transfer mechanism, which facilitates the inter-reservoir dissemination of resistance determinants across anthropogenic, zoogenic, and environmental microbiomes. This study investigated a multidrug-resistant Enterobacter hormaechei strain GS32 isolated from a deceased 180-day-old laying hen. Antimicrobial susceptibility testing, whole-genome sequencing, and comparative genomics were employed to analyze resistance profiles, plasmid architecture, and genetic mobility. Conjugation assays assessed plasmid transferability. Results revealed E. hormaechei GS32 harbored a 255 kb IncHI2/IncHI2A plasmid carrying mcr-9.4(pGS32-1) within a conserved transposon (IS1R-qseB/qseC-wbuC-mcr-9.4-IS903B) alongside 14 additional resistance genes [e.g., tet(D), mph(A), and sul2] and heavy metal resistance determinants. The pGS32-1 demonstrated high similarity to those in Salmonella spp. and Citrobacter freundii, suggesting cross-species transmission. Conjugation to EC600 occurred efficiently (frequency: [7.92 ± 0.75] × 10−²). To our knowledge, the present study provides the first evidence of the presence of an IncHI2 carrying mcr-9.4 in E. hormaechei isolated from poultry. The pGS32-1 was frequently found in Enterobacter sp. (including E. hormaechei and Enterobacter cloacae), Salmonella sp., and other bacteria such as C. freundii and Leclercia adecarboxylata, indicating the cross-species transmission capability of IncHI2 plasmids, highlighting its role in disseminating polymyxin resistance across ecological niches. These findings underscore the urgent need for enhanced antimicrobial resistance surveillance in livestock and stricter antibiotic stewardship to mitigate the emergence of a multidrug-resistant pathogen under the One Health framework.IMPORTANCEPolymyxin, as the last-line therapeutic agent against carbapenem-resistant Gram-negative bacterial infections, is facing increasing clinical challenges due to the emergence of novel resistance mechanisms. In this study, a strain of Enterobacter hormaechei GS32 harboring an IncHI2/IncHI2A-type plasmid (pGS32-1) was isolated from deceased laying hens. This plasmid carries a multidrug resistance gene cluster, including mcr-9.4, and exhibits high-efficiency conjugative transfer capability. The mcr-9.4 gene is located within a conserved transposon structure (IS1R-qseB/qseC-wbuC-mcr-9.4-IS903B), colocalized with other resistance genes on the plasmid, suggesting its potential integration as a more complex transposon substructure into this plasmid type. Previous studies have demonstrated that IncHI2-type plasmids are predominantly distributed among Enterobacteriaceae species such as Klebsiella pneumoniae and Salmonella spp. Notably, pGS32-1 exhibits high homology with plasmids identified in Salmonella spp. and Citrobacter freundii, indicating the cross-species transmission potential of IncHI2/IncHI2A-type plasmids and their role in expanding the reservoir of resistance genes.

【 授权许可】

CC BY   
Copyright © 2026 Liu et al.

【 图 表 】

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