Escherichia coli O157: H7 and its significance in foods

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Abstract

Escherichia coli O157:H7 was conclusively identified as a pathogen in 1982 following its association with two food-related outbreaks of an unusual gastrointestinal illness. The organism is now recognized as an important cause of foodborne disease, with outbreaks reported in the U.S.A., Canada, and the United Kingdom. Illness is generally quite severe, and can include three different syndromes, i.e., hemorrhagic colitis, hemolytic uremic syndrome, and thrombotic thrombocytopenic purpura. Most outbreaks have been associated with eating undercooked ground beef or, less frequently, drinking raw milk. Surveys of retail raw meats and poultry revealed E. coli O157:H7 in 1.5 to 3.5% of ground beef, pork, poultry, and lamb. Dairy cattle, especially young animals, have been identified as a reservoir. The organism is typical of most E. coli, but does possess distinguishing characteristics. For example, E. coli O157:H7 does not ferment sorbitol within 24 h, does not possess beta-glucuronidase activity, and does not grow well or at all at 44-45.5 degrees C. The organism has no unusual heat resistance; heating ground beef sufficiently to kill typical strains of salmonellae will also kill E. coli O157:H7. The mechanism of pathogenicity has not been fully elucidated, but clinical isolates produce one or more verotoxins which are believed to be important virulence factors. Little is known about the significance of pre-formed verotoxins in foods. The use of proper hygienic practices in handling foods of animal origin and proper heating of such foods before consumption are important control measures for the prevention of E. coli O157:H7 infections.

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Escherichia coli that cause diarrhea: enterotoxigenic, enteropathogenic, enteroinvasive, enterohemorrhagic, and enteroadherent.

Steven LeVine (1987)

There are four major categories of diarrheagenic Escherichia coli: enterotoxigenic (a major cause of travelers' diarrhea and infant diarrhea in less-developed countries), enteroinvasive (a cause of dysentery), enteropathogenic (an important cause of infant diarrhea), and enterohemorrhagic (a cause of hemorrhagic colitis and hemolytic uremic syndrome). Besides manifesting distinct clinical patterns, these categories of E. coli differ in their epidemiology and pathogenesis and in their O:H serotypes. Common features (albeit distinct for each category) include plasmid-encoded virulence properties, characteristic interactions with intestinal mucosa, and elaboration of various types of enterotoxins or cytotoxins. A less-well-defined fifth category of diarrheagenic E. coli is that of enteroadherent E. coli, so far identifiable only by their pattern of adherence to Hep-2 cells in tissue culture.

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A severe outbreak of Escherichia coli O157:H7--associated hemorrhagic colitis in a nursing home.

Eric Carlson, J Hockin, E C Krishnan … (1987)

In September 1985, an outbreak of Escherichia coli O157:H7 enteritis affected 55 of 169 residents and 18 of 137 staff members at a nursing home. The outbreak was characterized by two phases: a primary wave whose source was probably a contaminated sandwich meal and a secondary wave compatible with person-to-person transmission of infection. Among the elderly residents, the incubation period was 4 to 9 days (mean, 5.7 +/- 1.2). Older age and previous gastrectomy increased the risk of acquiring the infection (P = 0.01 and 0.03, respectively). Antibiotic therapy during exposure was associated with acquiring a secondary infection (P = 0.001). Hemolytic uremic syndrome developed in 12 affected residents (22 percent), 11 of whom died. Overall, 19 (35 percent) of the affected residents died, 17 (31 percent) from causes attributable to their infection. Antibiotic therapy after the onset of symptoms was associated with a higher case fatality rate in the more severe cases, possibly because patients with more severe disease tended to be treated with antibiotics. There were no complications or deaths among the affected members of the staff. Evidence of infection by verotoxin-producing E. coli O157:H7 was detected in 30 of 70 cases on the basis of isolation of this organism or demonstration of free verotoxin in stools. All isolates belonged to the same phage type. The high morbidity and mortality associated with this condition emphasize the need for proper food hygiene, rapid identification of outbreaks of disease, and prompt institution of infection-control techniques among the institutionalized elderly.

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A DNA probe to identify enterohemorrhagic Escherichia coli of O157:H7 and other serotypes that cause hemorrhagic colitis and hemolytic uremic syndrome.

H Lior, V Prado, H. Karch … (1987)

Enterohemorrhagic Escherichia coli (EHEC) cause hemorrhagic colitis and hemolytic uremic syndrome (HUS), make potent cytotoxins (Verotoxins [VT] or Shiga-like toxins), and possess a plasmid (approximately 60 megadaltons) that encodes a new fimbrial antigen and promotes attachment to epithelial cells. We evaluated the use of a DNA probe, prepared from a 3.4-kilobase segment of the EHEC plasmid, to detect EHEC. The probe hybridized with 106 (99%) of 107 O157:H7 and 34 (77%) of 44 O26:H11, VT-positive strains from patients with colitis, HUS, and diarrheal disease and hybridized with 21 (81%) of 26 VT-positive E. coli of serotypes other than O157:H7 or O26:H11 from patients with hemorrhagic colitis and HUS. We examined 601 other strains, including 18 serotype O26 isolates of H types other than H11, 306 enteropathogenic E. coli, 60 enteroinvasive E. coli, 119 enterotoxigenic E. coli, and 20 isolates from the urinary tract and 77 isolates from the normal intestinal flora; only one (O127:H-) was positive (specificity, 99.8%). Serotype O26:H11, previously considered a classic enteropathogenic E. coli serotype, is now shown to be EHEC.