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Updated: May 19, 2026

Characterization of a Pathogenic Escherichia coli Strain Derived from Oreochromis spp. Farms Using Whole-Genome Sequencing
Published on: December 23, 2022
First description of ColE-type plasmid in Aeromonas spp. carrying quinolone resistance (qnrS2) gene
J E Han1, J H Kim, C H Choresca
1Laboratory of Aquatic Animal Medicine, College of Veterinary Medicine and Research Institute for Veterinary Science, Seoul National University, Seoul, Korea.
Aims:
Isolation and full sequence analysis of ColE-type plasmid, which carries the qnrS2 gene.
Methods And Results:
Quinolone resistance (qnrS2) gene-carrying plasmids were isolated from Aeromonas sobria and Aeromonas hydrophila strains, and plasmid sequencing was achieved by a primer-walking approach. The total sizes of these plasmids (pAQ2-1 and pAQ2-2) were 6900 bp and 6903 bp, respectively, and they were 99·1% identical to each other. The genes (oriV and repA) for plasmid replication were organized similar to the corresponding genes in the ColE2-type plasmids, pAsa3 and pAsa1, isolated from Aeromonas salmonicida subsp. salmonicida, but the gene (mobA) for mobilization was homologue to ColE1-type plasmid (pAsa2) from Aer. salmonicida subsp. salmonicida. Additionally, the qnrS2 gene was part of a mobile insertion cassette element in the plasmid.
Conclusions:
Two plasmids were assumed to be the same plasmid, and this identification of a plasmid-mediated qnrS2 gene from the two different strains underlines a possible diffusion of these resistance determinants in an aquaculture system.
Significance And Impact Of The Study:
This is the first finding of the ColE-type plasmid carrying the qnrS2 gene.
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