Genomic Characterization of a Multidrug-Resistant ST88 Enterotoxigenic/Shiga Toxin-Producing Hybrid Escherichia coli Isolated from a Pig in Korea

Enterotoxigenic/Shiga toxin-producing hybrid Escherichia coli (ETEC/STEC) strains harbor virulence determinants of both pathotypes and may carry multiple antimicrobial resistance determinants. We characterized the complete genome and antimicrobial resistance profile of the ETEC/STEC hybrid strain GCUHS-1A isolated from a post-weaning pig in Korea. Molecular and bioinformatic analyses identified virulence and antimicrobial resistance genes, plasmid replicons, prophages, serotype, and sequence type, while antimicrobial susceptibility was assessed by minimum inhibitory concentration testing. The 5.64-Mb genome comprised one chromosome and seven plasmids. GCUHS-1A was assigned to sequence type 88 (ST88) and serotype O-untypable:H11. Plasmid-borne eltAB and F18ac fimbrial genes and prophage-encoded stx2e confirmed its ETEC/STEC hybrid profile. The strain was resistant to 16 antimicrobial agents and carried multiple acquired resistance genes and quinolone resistance-associated gyrA substitutions. Despite cephalosporin resistance and a positive extended-spectrum β-lactamase (ESBL) phenotypic confirmatory test, no acquired ESBL or plasmid-mediated ampC genes were detected. To our knowledge, GCUHS-1A is the first completely sequenced porcine-associated ST88 ETEC/STEC hybrid strain reported in Korea. These findings provide a genomic reference for porcine-associated ST88 ETEC/STEC hybrid strains, illustrate the modular coexistence of virulence and multidrug resistance determinants, and highlight the value of integrating phenotype and genomic resistance analyses.