AUTHOR=Lee Woojung , Ha Jina , Choi Jaehyun , Jung Yewon , Kim Eiseul , An Eun Sook , Kim Seung Hwan , Shin Hakdong , Ryu Sangryeol , Kim Soon Han , Kim Hae-Yeong 

TITLE=Genetic and virulence characteristics of hybrid Shiga toxin-producing and atypical enteropathogenic Escherichia coli strains isolated in South Korea

JOURNAL=Frontiers in Microbiology

VOLUME=15

YEAR=2024

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2024.1398262

DOI=10.3389/fmicb.2024.1398262

ISSN=1664-302X

ABSTRACT=<sec id="sec1"><title>Introduction</title><p>The predominant hybrid pathogenic <italic>E. coli</italic>, enterohemorrhagic <italic>E. coli</italic> (EHEC), combines characteristics of Shiga toxin-producing <italic>E. coli</italic> (STEC) and enteropathogenic <italic>E. coli</italic> (EPEC), contributing to global outbreaks with severe symptoms including fatal consequences. Since EHEC infection was designated as a notifiable disease in 2000 in South Korea, around 2000 cases have been reported, averaging approximately 90 cases annually.</p></sec><sec id="sec2"><title>Aim</title><p>In this work, genome-based characteristic analysis and cell-based assay of hybrid STEC/aEPEC strains isolated from livestock feces, animal source foods, and water in South Korea was performed.</p></sec><sec id="sec3"><title>Methods</title><p>To identify the virulence and antimicrobial resistance genes, determining the phylogenetic position of hybrid STEC/aEPEC strains isolated in South Korea, a combination of real-time PCR and whole-genome sequencing (WGS) was used. Additionally, to assess the virulence of the hybrid strains and compare them with genomic characterization, we performed a cell cytotoxicity and invasion assays.</p></sec><sec id="sec4"><title>Results</title><p>The hybrid STEC/aEPEC strains harbored <italic>stx</italic> and <italic>eae</italic> genes, encoding Shiga toxins and <italic>E. coli</italic> attachment/effacement related protein of STEC and EPEC, respectively. Furthermore, all hybrid strains harbored plasmid-carried enterohemolysin(<italic>ehxCABD</italic>), a key virulence factor in prevalent pathogenic <italic>E. coli</italic> infections, such as diarrheal disease and hemolytic-uremic syndrome (HUS). Genome-wide phylogenetic analysis revealed a close association between all hybrid strains and specific EPEC strains, suggesting the potential acquisition of Stx phages during STEC/aEPEC hybrid formation. Some hybrid strains showed cytotoxic activity against HeLa cells and invasive properties against epithelial cells. Notably, all STEC/aEPEC hybrids with sequence type (ST) 1,034 (<italic>n</italic> = 11) exhibited higher invasiveness than those with E2348/69. This highlights the importance of investigating potential correlations between STs and virulence characteristics of <italic>E. coli</italic> hybrid strains.</p></sec><sec id="sec5"><title>Conclusion</title><p>Through genome-based characterization, we confirmed that the hybrid STEC/aEPEC strains are likely EPEC strains that have acquired STEC virulence genes via phage. Furthermore, our results emphasize the potential increased danger to humans posed by hybrid STEC/aEPEC strains isolated in South Korea, containing both <italic>stx</italic> and <italic>eaeA</italic>, compared to STEC or EPEC alone.</p></sec>