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E. coli strain O157:H7

Dateline: 03/06/00

By Alan Bruzel

Background

Bacterial strains of Escherichia coli are categorized by their surface antigens; O and H antigen serotypes are one means of classification. E. coli strain O157:H7, a pathogen first seen in 1982 during an outbreak of bloody diarrhea (hemorrhagic colitis) that was linked to undercooked hamburger, appears to harmlessly live in the gut of cattle, just as a strain of Salmonella (also pathogenic to humans) resides harmlessly in the ovaries of chickens. The trouble arises when these bacteria move from their natural hosts to the bodies of humans. From more than 5,200,000 total estimated bacterial cases of foodborne illness per year in the United States, about 73,000 are due to E. coli O157:H7, and about 1,400,000 are due to nontyphoidal Salmonella.

Just What Toxins Are in E. coli O157:H7?

The E. coli ordinarily in our intestines and the pathogenic E. coli O157:H7 differ in significant ways. The O157:H7 strain contains genes that code for production of one or more Shiga-like toxins (so named because of their structural similarity to toxins produced by the bacterium Shigella dysenteriae) that are inhibitors of protein synthesis. These genes are not part of everyday E. coli, but were brought into ancestral E. coli O157:H7 by bacterial viruses carrying these genes. To make matters worse, O157:H7 also carries several different plasmids (plasmids are autonomous strands of DNA) whose genes code for virulence factors, some of which may facilitate attachment of E. coli O157:H7 to human cells.

How Does One Prevent E. coli O157:H7 Infection?

This bacterium may not only be present in meat and dairy products, but may be found in any food – animal or vegetable – that has accidentally come in contact with cattle intestines or their contents. Infected humans also may spread the bacteria to uninfected individuals. It is believed that from two to 10 living E. coli O157:H7 bacteria are all that are necessary for a productive infection. The operative word in the last sentence is "living." Dead bacteria cannot reproduce. Thoroughly cook your ground beef.

What the Web Has to Say about:
E. coli strain O157:H7

Chlorine Inactivation of Escherichia coli O157:H7
U.S. Environmental Protection Agency report describes that E. coli O157:H7 and nonpathogenic strains of E. coli are both destroyed by standard chlorination disinfection of water supplies. Published in Emerging Infectious Diseases, a journal from the Centers for Disease Control and Prevention.

DNA Sequencing for E. coli O157:H7
Identification of E. coli O157:H7 by detecting specific regions of its Shiga-like toxin genes and of a plasmid the bacterium harbors. From Pina M. Fratamico, U.S. Department of Agriculture.

E. coli O157:H7, Other Verotoxin-Producing Escherichia coli, and Hemolytic-Uremic Syndrome in Childhood
Article from the Infectious Diseases and Immunization Committee, Canadian Pediatric Society, describes symptoms, treatment, and prevention of E. coli O157:H7 infection.

Emerging Foodborne Diseases: An Evolving Public Health Challenge
Robert V. Tauxe, Centers for Disease Control and Prevention, presents analytical methods designed to identify organisms responsible for outbreaks of foodborne illnesses. Published in Emerging Infectious Diseases.

Enterohemorrhagic Escherichia coli
Investigations into the bacteriophage and plasmids residing in these bacterial strains. From the Bayerische Julius-Maximilians-Universität Würzburg.

Escherichia coli O157:H7
Facts, figures, and resources concerning this pathogen. From the Bad Bug Book, U.S. Food and Drug Administration.

Escherichia coli Serotype O157:H7: Novel Vehicles of Infection and Emergence of Phenotypic Variants
Article by Peter Feng, U.S. Food and Drug Administration, cautions that contaminated bovine products are not the only route of foodborne infection for E. coli O157:H7, and that variants may require specific screening protocols. Published in Emerging Infectious Diseases.

Foodborne Illness: E. coli O157:H7
Sources of infection and complications after infection. From About.com's Nursing Guide.

Food-Related Illness and Death in the United States
Compilation from the Centers for Disease Control and Prevention presents itemization of bacterial, parasitic, and viral foodborne infections in the US. Published in Emerging Infectious Diseases.

Molecular Population Genetic Analysis of Emerged Bacterial Pathogens: Selected Insights
James M. Musser, Baylor College of Medicine, provides evidence that E. coli strain O157:H7 and the infantile diarrhea strain E. coli O55:H7 descended from a common ancestral line. Published in Emerging Infectious Diseases.

Vero Cytotoxin-Producing Escherichia coli O157 Outbreaks in England and Wales, 1995: Phenotypic Methods and Genotypic Subtyping
Investigators from the Central Public Health Laboratory, and the Communicable Disease Surveillance Center, London, UK describe means of differentiating different E. coli O157 strains by using DNA analysis. Published in Emerging Infectious Diseases.

Virulence Factors Encoded by Conjugative R Plasmids of Escherichia coli O157 Isolates of Cattle
Antibiotic resistance factors are present in the plasmid of E. coli O157:H7. From Soon-Pak-Shinji Yue and Lisa K. Nolan, North Dakota State University.

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