Genotypic Changes in Enterohemorrhagic Escherichia coli During Human Infection

The chapter begins with an overview of epidemiology and clinical pathogenesis of Enterohemorrhagic Escherichia coli (EHEC). EHEC causes diarrhea, bloody diarrhea, and hemolytic-uremic syndrome (HUS). The major virulence factor of EHEC responsible for the microvascular endothelial injury is Shiga toxin (Stx). In additon to Stx, several other potential virulence determinants have been identified in EHEC. Next, the chapter focuses on genomes of EHEC. The lability of horizontally acquired genomic elements, such as pathogenicity islands, and especially of bacteriophages, increases the possibility of genomic alterations during human infections. Most EHEC strains possess one or more large plasmids. To investigate genetic changes of EHEC in patients with HUS, consecutive stool samples from such patients was analyzed by detecting stx and eae genes and by using a cytotoxicity assay to detect free Stx. Further, the chapter talks about interserotype differences in conversion of EHEC to EHEC-LST, and consequences of in vivo genetic changes in EHEC. To identify both EHEC and EHEC-LST in stool samples, detection of stx must be complemented by detection of stx-independent target(s) which are common to both pathotypes. Genetic changes in EHEC during infection might influence clinical outcome and have impacts on diagnosis, epidemiology, and evolution. For clinicians, awareness of a potential conversion of the pathotype of the infecting EHEC during infection is essential in making decisions about correct management of the patients and appropriate therapies.