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Chapter 12 : Enterohemorrhagic Escherichia coli
Category: Applied and Industrial Microbiology; Food Microbiology
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.
Number of E. coli O157:H7 outbreaks in the United States by year, 1982–2002 (n = 350), reproduced from reference 47 .
Transmission routes of E. coli O157:H7 outbreaks in the United States by year, 1982–2002, reproduced from reference 47 .
Vehicles of foodborne E. coli O157:H7 outbreaks in the United States by year, 1982–2002, reproduced from reference 47 .
Schematic illustration of A/E lesion formation in EHEC, modified based on references 8 and 56 . (A) A/E translocation of effector proteins through TTSS that forms a pore through the membranes of EHEC. EHEC translocate a number of proteins: EspB and EspD, which form a translocon in the plasma membrane; the cytoplasmic proteins EspF, EspG, and Map; the translocated intimin receptor Tir, which inserts into the plasma membrane; and other unidentified effectors. (B) Formation of EHEC pedestal. EHEC intimately attaches to the host cell through intimin-Tir binding. The binding triggers the formation of actin-rich pedestals beneath adherent bacteria after Wiskott-Aldrich syndrome protein (WASP) and the heptameric actin-related protein Arp2/3 are recruited to the pedestal tip.
Genetic organization of the EHEC LEE and EHEC prophages CP-933U, CP-933K, and CP-933P, reproduced from reference 21 .
TTSS apparatus of EHEC. The basal body of the TTSS is composed of the secretin EscC, the inner membrane proteins EscR, EscS, EscT, EscU, and EscV, and the EscJ lipo-protein, which connects the inner and outer membrane ring structures. EscF constitutes the needle structure, whereas EspA subunits polymerize to form the EspA filament. EspB and EspD form the translocation pore in the host cell plasma membrane, connecting the bacteria with the eukaryotic cell via EspA filaments. The cytoplasmic ATPase EscN provides the energy to the system by hydrolyzing ATP molecules into ADP. SepD and SepL have been represented as cytoplasmic components of the TTSS. (Reproduced from reference 21 .)
Serotypes of non-O157 Shiga toxin-producing E. coli recovered from patients with hemorrhagic colitis and/or HUS a
Comparison of D values for E. coli O157:H7 and Salmonella spp. in ground beef
Outbreaks and cases of E. coli O157 infection by transmission route, 1982–2002 a
Representative foodborne and waterborne outbreaks of E. coli O157:H7 and other EHEC infections a
List of effector proteins of EHEC a
Nomenclature and biological characteristics of Shiga toxins (Stx) a