Enterohemorrhagic Escherichia coli

Diarrheagenic Escherichia coli isolates are categorized into specific groups (pathotypes) based on virulence properties, mechanisms of pathogenicity, clinical syndromes, and distinct O:H serotypes. This chapter focuses on enterohemorrhagic E. coli (EHEC), which among the E. coli strains that cause foodborne illness in the United States, is the most significant group based on frequency and severity of illness. Since E. coli O157:H7 is the most common serotype of the EHEC and because more is known about this serotype than other serotypes of EHEC, the chapter focuses on E. coli O157:H7. E. coli O157:H7 strains isolated from humans, animals, and food have developed resistance to multiple antibiotics, with streptomycin-sulfisoxazoletetracycline being the most common resistance profile. Details of many reported foodborne and waterborne outbreaks of EHEC infections are provided in the chapter. The nomenclature of the Shiga toxins (Stx) family and their important characteristics are listed. Stx and Stx1 production is negatively regulated at the transcriptional level by an iron-Fur protein corepressor complex which binds at the stx1 promoter but is unaffected by temperature. The severity of the illness it causes combined with its apparent low infectious dose qualifies E. coli O157:H7 to be among the most serious of known foodborne pathogens. E. coli O157: H7 is still by far the most important serotype of Shiga toxin-producing E. coli (STEC) in North America. Isolation of non-O157:H7 STEC requires techniques not generally used in clinical laboratories; hence, these bacteria are infrequently sought or detected in routine practice.