Enterohemorrhagic Escherichia coli (EHEC) has emerged as an important foodborne pathogen and a predominant cause of hemorrhagic colitis (HC) in humans. This illness, with characteristic symptoms of bloody diarrhea and severe abdominal cramps, may progress into the potentially life-threatening complication known as hemolytic uremic syndrome (HUS).[1,2]
The pathogenicity of EHEC is thought to be attributable to the production of Shiga toxins (Stx), also referred to as Verotoxins, which inhibit protein synthesis by interfering with the functions of the 23S rRNA. Stx1 and Stx2 are most often produced by EHEC strains causing illness, but Stx2 is most often implicated in HUS; hence, it appears to be more important in human infections. There are several variants of Stx2 (Stx2c, Stx2d, Stx2e, Stx2f, etc.), and although many of these are produced by animal or environmental strains, recent evidence suggest that some variants may also cause human illness. It is estimated that there are over 200 E. coli serotypes that produce Stx. Collectively known as Shiga toxin-producing E. coli (STEC), many of these may be found in the feces of animals or healthy humans and have not been implicated in illness. Therefore EHEC is a small subset of STEC composed of strains sharing the same clinical, epidemiological, and pathogenic features that can be distinguished from STEC via the presence of other virulence traits.
While many EHEC serotypes, including O157:H7, O111:H8, O26:H11, O103:H2, O113:H2, O104:H21, and their nonmotile (NM) counterparts, have been implicat ed in illness, the O157:H7-type strain is still the predominant pathogen causing most of the EHEC foodborne infections and outbreaks worldwide. The O157:H7 group is clonal and only distantly related to other E. coli, except for enteropathogenic E. coli (EPEC) of O55:H7 sero-type. Enterohemorrhagic E. coli strains are serologically and genetically diverse with significant phenotypic and genetic diversity observed even within serologically identical groups, such as with the O157:H7 group. As a consequence, the development of diagnostic assays for EHEC can be complicated. However, these difficulties can be overcome by using polymerase chain reaction (PCR) technology that can differentiate variations within genetic sequences to the level of single nucleotide polymorphisms.
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