THE E. COLI O157:H7 BACTERIA
Sources, Characteristics, and Identification
Escherichia coli (E. coli) is an archetypal commensal bacterial species that lives in mammalian intestines. E. coli O157:H7 is one of thousands of serotypes E. coli.[1] The combination of letters and numbers in the name of E. coli O157:H7 refers to the
The Public Health Agency of Canada is collaborating with federal and provincial public health partners to investigate an outbreak of Escherichia coli, called E. coli O121 that has now been linked to Robin Hood All Purpose Flour, Original. The Canadian Food Inspection Agency (CFIA) has issued a food recall warning advising Canadians of the
The Chicago Department of Public Health (CDPH) continues to work with the owners and staff of Carbón Live Fire Mexican Grill at 300 W. 26th Street as part of our ongoing investigation into an outbreak of Shiga toxin-producing E. coli (STEC). To date, 50 residents have been identified as contracting STEC related to this outbreak.
Washington Beef, LLC, a Toppenish, Wash., establishment, is recalling 1,620 pounds of boneless beef trim product that may be contaminated with E. coli O157:H7, the U.S. Department of Agriculture’s Food Safety and Inspection Service (FSIS) announced today.
The following boneless beef product produced on Nov. 28, 2012, is subject to recall:
60 lb. bulk packs
Minnesota State health officials have identified green whole head cabbage as the likely source of an E. coli O111 outbreak that sickened 15 people in Minnesota in July. The cabbage was likely contaminated at some point prior to distribution to restaurants.
Routine monitoring by the Minnesota Department of Health (MDH) identified the 15 cases of
Melanie Dunstan became the third California resident to file a lawsuit against Glass Onion Catering this week. The lawsuit alleges that the plaintiff fell ill with an E. coli O157:H7 infection after eating a salad made by Glass Onion Catering and sold by Trader Joe’s in early November of 2013. Ms. Dunstan is represented by
FSIS was notified of an investigation of E. coli O157:H7 illnesses by the Wisconsin Division of Public Health on Jan. 10, 2013. Working in conjunction with the Wisconsin Division of Public Health, three case-patients with the outbreak strain have been identified in the state with illness onset dates ranging from Dec. 29, 2012 to Jan.
The Division of Public Health of the N.C. Department of Health and Human Services in collaboration with Local Health Departments is investigating an outbreak of E. coli infection in 106 people who attended the Cleveland County Fair. Preliminary findings suggest animal exposure may be the source of this outbreak.
As of 2 p.m., 64 children*
KMOV’s Maggie Crane reports that a 23-year-old is dead after she got E. coli, possibly after eating at a local restaurant. Her family is now asking for an investigation into the restaurant.
Ciera Brookfield told her family that she felt sick after eating at a Chinese restaurant in Overland.
Ciera was just 23 when she
Bad Bug Book – Foodborne Pathogenic Microorganisms and Natural Toxins – Second Edition
1. Organism
Like generic E. coli, toxin-producing Shiga- toxigenic Escherichia coli (STEC) are Gram- negative, rod-shaped bacteria, but are characterized by the production of Shiga toxins (Stx). Depending on the reference cited, there are 200 to 400 STEC serotypes, many of which have not been implicated in human illness; however, a subset of STEC called enterohemorrhagic Escherichia coli (EHEC), the topic of this chapter, includes only those that cause serious illness. Serotype O157:H7 is the prototypic EHEC strain.
Although O157:H7 is currently the predominant strain and accounts for ~75% of the EHEC infections worldwide, other non-O157 EHEC serotypes are emerging as a cause of foodborne illnesses. In the United States a group often referred to as the “big 6” (O111, O26, O121, O103, O145, and O45) accounts for the majority of the non-O157:H7 serotypes isolated from clinical infections and, therefore, is currently a focus of concern. However, other EHEC serotypes, such as O113, O91, and others, also can cause severe illness. As a result, the non-O157 EHEC serotypes of public health concern can change quickly, depending on outbreak incidents, and can vary with countries and geographic regions.
A recent example is the large outbreak, in 2011, that was centered in Germany, but also affected various other countries in the European Union. The pathogen was identified as an E. coli strain of serotype O104:H4 that produced Shiga toxin and, therefore, was thought to be an EHEC. However, genetic analysis showed that this pathogen had 93% genetic homology with a strain of Enteroaggregative E. coli (EAEC), which is known for causing persistent diarrhea in under- developed countries, but has seldom been implicated in major foodborne incidents. Hence, the O104:H4 strain that caused the outbreak appears to be an EAEC strain that acquired the ability to produce Shiga toxin.
Currently, it is difficult to determine which serotypes of E. coli are EHEC and equally challenging to predict the emergence of strains that can acquire the genes for Shiga toxin production or other virulence factors and so cause human illness. EHEC are characterized by:
There are also several other putative virulence factors, including enterohemolysin, but the role of these factors in pathogenesis remains undetermined.
2. Disease
3. Frequency
It is estimated that there are about 63,000 cases of EHEC infections in the U.S. yearly. Ground beef and beef products continue to be implicated in most infections; however, contaminated produce increasingly has been implicated as a vehicle. As for STEC non-O157, the CDC estimates that 112,752 cases, per year, are attributed to foodborne illness in the U.S.
EHEC O157:H7 was first identified in an outbreak, in 1982, in which hamburgers from a fast- food restaurant were the vehicle. In 1991 (sic, 1992-1993), hamburgers from fast-food restaurants were implicated in another outbreak, which affected about 700 people in four states. In the mid 1990s, a large outbreak was traced to unpasteurized juices. The largest O157:H7 outbreak on record took place in Japan; radish sprouts were implicated and about 10,000 people were affected. Since then, O157:H7 has been implicated in numerous outbreaks that involved lettuce, salads, various types of sprouts, and, in 2006, bagged spinach. In 2009, an O157:H7 outbreak in the U.S. was traced to frozen, raw cookie dough.
About a dozen non-O157:H7 EHEC outbreaks have been recorded in the U.S., but incidences may be underestimated due to lack of routine testing and appropriate testing methods.
4. Sources
Raw or undercooked ground beef and beef products are the vehicles most often implicated in O157:H7 outbreaks. Earlier outbreaks also implicated consumption of raw milk. O157:H7 can develop acid tolerance, as evidenced by infections in which acid foods (<pH4.6) were implicated, such as yogurt, mayonnaise, fermented sausages, cheeses, and unpasteurized fruit juices.
Various water sources, including potable, well, and recreational water, also have caused EHEC infections, as has contact with animals at farms or petting zoos.
Produce, including bagged lettuce, spinach, and alfalfa sprouts, increasingly is being implicated in O157:H7 infections.
Interestingly, infections in the U.S. by non-O157:H7 EHEC has been caused by many of these same vehicles, but, as of this writing, beef products have seldom been implicated.
Person-to-person transmission of infection is well documented.
Additional information is available from “Escherichia coli Serotype O157:H7: Novel Vehicles of Infection and Emergence of Phenotypic Variants,” by Dr. Peter Feng, FDA. Emerging Infectious Diseases (1995) 1(2)
5. Diagnosis
Unlike generic E. coli, EHEC O157:H7 do not ferment the sugar sorbitol, so an effective method is to plate patient’s bloody diarrhea samples onto sorbitol MacConkey medium to screen for sorbitol non-fermenting isolates. These are then typed serologically using antibodies to the O157 and the H7 antigens. However, as other EHEC serotypes are increasingly causing illness, clinical samples are now simultaneously tested for the presence of Stx using commercially-available antibody kits. Any STEC strains found are then serotyped and identified. There are also many PCR assays specific for Stx genes that may be used for screening clinical samples.
6. Target Populations
All people are believed to be susceptible to hemorrhagic colitis, but young children and the elderly are more susceptible and at higher risk for the illness to progress to more severe complications. Others with weak immune systems also are at risk, such as people with some chronic diseases or AIDS, and people on immunosuppressive medications; for example, some drugs used for arthritis and cancer chemotherapy.
7. Food Analysis
Presence of EHEC O157:H7 in foods can be determined by plating culture enrichment of food samples onto selective and differential media. Unlike typical E. coli, O157:H7 do not ferment sorbitol and are negative with the MUG assay, so these tests are commonly used to distinguish O157:H7 strains from other E. coli prior to serological testing for the O157 and H7 antigens and also for the presence of Stx genes by PCR. Molecular assays also exist that can specifically detect O157:H7 strains using unique mutational markers.
Detection of non-O157:H7 EHEC, however, is more complex, due to the lack of unique traits. For non-O157 EHEC, food enrichment is first screened for Shiga toxin using an antibody assay or for Stx genes by PCR. Enrichment cultures that are positive for Stx are plated on agar media, and multiple isolates are then tested for Stx genes, in order to obtain a pure culture isolate. These putative STEC isolates are then retested for virulence genes and their serotype determined. This process is both time-consuming and labor-intensive and may require screening hundreds of isolates.
There are numerous commercially-available kits to test for Stx, O157, and a few other EHEC serotypes. However, there are several Stx subtypes and many EHEC serotypes, and not all of these can be detected by commercial test kits. The Escherichia coli link to the FDA Bacteriological Analytical Manual, Chapter 4, provides a description of methods to test for common E. coli. Methods for EHEC and O157:H7 are described in Chapter 4a.
8. Examples of Outbreaks
For more information about recent outbreaks see the Centers for Disease Control and Prevention (CDC) Morbidity and Mortality Weekly Reports.
9. Other Resources
More information is available from the following sources.