The global emergence of hybrid diarrheagenic E. coli strains incorporating genetic markers from different pathotypes is a public health concern. Hybrids of Shiga toxin-producing and enterotoxigenic E. coli (STEC/ETEC) are associated with diarrhea and hemolytic uremic syndrome (HUS) in humans. In this study, we identified and characterized STEC/ETEC hybrid strains isolated from livestock feces (cattle and pigs) and animal food sources (beef, pork, and meat patties) in South Korea between 2016 and 2020. The strains were positive for genes from STEC and ETEC, such as stx (encodes Shiga toxins, Stxs) and est (encodes heat-stable enterotoxins, ST), respectively. The strains belong to diverse serogroups (O100, O168, O8, O155, O2, O141, O148, and O174) and sequence types (ST446, ST1021, ST21, ST74, ST785, ST670, ST1780, ST1782, ST10, and ST726). Genome-wide phylogenetic analysis revealed that these hybrids were closely related to certain ETEC and STEC strains, implying the potential acquisition of Stx-phage and/or ETEC virulence genes during the emergence of STEC/ETEC hybrids. Particularly, STEC/ETEC strains isolated from livestock feces and animal source foods mostly exhibited close relatedness with ETEC strains. These findings allow further exploration of the pathogenicity and virulence of STEC/ETEC hybrid strains and may serve as a data source for future comparative studies in evolutionary biology.

Hybrid strains Escherichia coli acquires genetic characteristics from multiple pathotypes and is speculated to be more virulent; however, understanding their pathogenicity is elusive. Here, we performed genome-based characterization of the hybrid of enteropathogenic (EPEC) and enterotoxigenic E. coli (ETEC), the strains that cause diarrhea and mortality in children. The virulence genes in the strains isolated from different sources in the South Korea were identified, and their phylogenetic positions were analyzed. The EPEC/ETEC hybrid strains harbored eae and est encoding E. coli attaching and effacing lesions and heat-stable enterotoxins of EPEC and ETEC, respectively. Genome-wide phylogeny revealed that all hybrids (n = 6) were closely related to EPEC strains, implying the potential acquisition of ETEC virulence genes during ETEC/EPEC hybrid emergence. The hybrids represented diverse serotypes (O153:H19 (n = 3), O49:H10 (n = 2), and O71:H19 (n = 1)) and sequence types (ST546, n = 4; ST785, n = 2). Furthermore, heat-stable toxin-encoding plasmids possessing estA and various other virulence genes and transporters, including nleH2, hlyA, hlyB, hlyC, hlyD, espC, espP, phage endopeptidase Rz, and phage holin, were identified. These findings provide insights into understanding the pathogenicity of EPEC/ETEC hybrid strains and may aid in comparative studies, virulence characterization, and understanding evolutionary biology.

A novel bacterial species, designated FBL11^T, was isolated from salted shrimp jeotgal, a traditional Korean fermented food sampled in the Republic of Korea. This strain showed the highest 16S rRNA gene sequence similarity to Psychrobacter halodurans strain F2608^T (NR_181578.1) at 98.3%. The genome size of strain FBL11^T was 3,294,493 bp with a G+C content of 42.5 mol%. Computation of relatedness indicates that strain FBL11^T shares the highest relatedness of 78.5% with Psychrobacter fulvigenes strain KC-40^T (NZ_CAJGZP01) and 25.2% with Psychrobacter piechaudii strain CIP110854^T (NZ_FUGE01), with values clearly below the cut-offs for species distinction. Polyphasic characterization using biochemical tests and matrix-assisted laser desorption/ionization time-of-flight MS analysis confirmed these findings. Strain FBL11^T grew at 10–30 °C (optimum, 20–30 °C) with 0–15% NaCl (w/v; optimum, 3–6%). Analysis of biosynthetic gene clusters responsible for secondary metabolite production revealed that strain FBL11^T generates unique products such as beta-lactone and redox-cofactors within this genus. Based on the genomic and phenotypic data obtained, we propose that strain FBL11^T represents a novel species, for which we propose the name Psychrobacter saeujeotis sp. nov. (type strain FBL11^T=KACC 23745^T=KCTC 8655^T=JCM 37231^T).

Yersinia enterocolitica is a psychrotrophic foodborne bacterium that can proliferate at refrigeration temperatures and is frequently associated with animal-source foods, raising concerns about food safety and public health. However, genomic data on Y. enterocolitica isolates from South Korea are limited, despite the increasing use of whole-genome sequencing (WGS) in bacterial surveillance. Herein, 91 Y. enterocolitica isolates recovered from chicken, pork, beef, and duck samples collected nationwide in 2024 were analyzed using WGS to elucidate their genomic diversity and genomic features. Phylogenomic analysis predicted all isolates as biotype 1A (sub-biotype 1Aa) and revealed substantial genetic diversity, comprising 27 sequence types and 43 core-genome types. Pan-genome analysis identified 11,230 gene clusters, revealing an open pan-genome in which accessory and unique gene clusters were assigned to predicted functional categories associated with metabolism, defense mechanisms, and stress responses. Although the canonical virulence plasmid pYV was absent, conserved chromosomal virulence-associated genes involved in adhesion (yapE), invasion (inv), secretion, and enterotoxicity (ystB) were detected. Antimicrobial resistance genes were predominantly intrinsic, particularly blaA and vat(F), whereas acquired resistance genes were identified sporadically. These findings provide a genomic baseline for biotype 1A Y. enterocolitica isolates recovered from animal-source foods in South Korea. The functional and public health significance of the detected virulence-associated loci requires further phenotypic investigation.

Clostridium perfringens is a major foodborne pathogen in which the genomic localization of the enterotoxin gene, cpe, plays an important epidemiological role. In this study, four isolates associated with independent foodborne outbreaks in South Korea were analyzed using complete genome sequencing. All isolates were cpe-positive, including three strains carrying chromosomal cpe (c-cpe) and one strain carrying plasmid-borne cpe (p-cpe). To provide a broader genomic context, complete genomes retrieved from the National Center for Biotechnology Information database were also analyzed. Most cpe-positive strains carried p-cpe, whereas c-cpe strains were relatively uncommon. Whole-genome analysis revealed a distinct separation between c-cpe and p-cpe strains based on conserved core-genome features and virulence gene profiles. In c-cpe strains, the cpe gene was consistently located between the nadA–C operon and a downstream nucleobase transporter gene and was flanked by IS1470 family transposases, suggesting a conserved chromosomal structure and a possible vertical inheritance. Conversely, p-cpe strains carried cpe on conserved pCW3-like plasmids, indicating that horizontal gene transfer mediated by a specific plasmid lineage contributes to cpe dissemination across diverse genetic backgrounds. Overall, these findings show that cpe localization is associated with distinct genomic patterns in C. perfringens.