Diverse structures of mcr-10-bearing plasmids and high colistin resistance in Enterobacter cloacae complex clinical isolates from South Korea.

Jong Hyun Shin; Min Seok Kim; Gi Uk Jeong; Kwan Soo Ko

doi:10.1016/j.ijantimicag.2026.107879

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Diverse structures of mcr-10-bearing plasmids and high colistin resistance in Enterobacter cloacae complex clinical isolates from South Korea.

Jong Hyun Shin·Min Seok Kim·Gi Uk Jeong·Kwan Soo Ko

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Abstract

BACKGROUND: The emergence of mcr-mediated colistin resistance in Enterobacter cloacae complex (ECC) poses a significant threat to antimicrobial therapy. Among mcr variants, mcr-10 has been identified in various environments, but its genetic diversity, structural context, and functional role in colistin resistance remain unclear. METHODS: We investigated 183 ECC isolates and identified 60 colistin-resistant strains through minimum inhibitory concentration (MIC) testing. The presence of mcr-10 was screened using reference genomes from NCBI, and whole plasmid sequencing was conducted on mcr-10-positive isolates. The genetic environment of mcr-10 was analyzed via synteny and structural annotation. RESULTS: Whole-plasmid sequencing of eight mcr-10-positive ECC isolates identified three replicon types among the mcr-10-harboring plasmids: IncFIB (n=3), IncFII (n=3), and IncFII/IncFIB (n=2). Although all plasmids shared the xerC-mcr-10 cassette, they lacked a conserved backbone and showed diverse genetic contexts with variable insertion sequences near mcr-10, indicating marked structural heterogeneity. No additional antimicrobial resistance genes were detected on these plasmids. When introduced into E. coli DH5α, the plasmids increased colistin MICs only modestly, whereas representative plasmids transferred into colistin-susceptible E. roggenkampii and E. kobei conferred high-level resistance comparable to that of the parental mcr-10-positive isolates. Consistently, qRT-PCR showed higher mcr-10 expression in ECC transformants than in E. coli under colistin exposure, supporting a hostdependent effect on mcr-10-mediated colistin resistance. CONCLUSION: These findings highlight the diversity of mcr-10-carrying plasmids and suggest that mcr-10-mediated colistin resistance is shaped by the host genetic background. Further studies are needed to clarify the mechanisms underlying mcr-10 expression.

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Colistin Enterobacter cloacae Plasmids Microbial Sensitivity Tests Anti-Bacterial Agents Drug Resistance, Bacterial Humans Republic of Korea Enterobacteriaceae Infections Bacterial Proteins Genetic Variation Extrachromosomal DNA Replicon Colistin resistance Enterobacter cloacae complex Plasmid mcr-10 Journal Article

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Jong Hyun Shin, Min Seok Kim, Gi Uk Jeong, Kwan Soo Ko. 2026-06-11. Diverse structures of mcr-10-bearing plasmids and high colistin resistance in Enterobacter cloacae complex clinical isolates from South Korea.. https://doi.org/10.1016/j.ijantimicag.2026.107879

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Journal Article resource Anti-Bacterial Agents subject Bacterial Proteins subject Drug Resistance, Bacterial subject Extrachromosomal DNA subject Genetic Variation subject Humans subject Journal Article subject Microbial Sensitivity Tests subject Plasmids subject

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