Why is the Finding of Generic E. coli a Red Flag?

There has been some confusion with the generic E. coli reference range. The following is a description of the specific types of pathogenic E. coli, most of which would be included in the test for generic E. coli. Pathogenic Escherichia coli, commonly referred to as E. coli, is a member of the normal microflora of the intestinal tract of warm-blooded animals including humans. These bacteria have a symbiotic relationship with the host and serve a useful function in the body by suppressing the growth of harmful bacterial species and by synthesizing appreciable amounts of vitamins.

However, several strains have developed specific virulent traits that enable them to cause a variety of diseases, ranging from diarrhea to hemolytic uremic syndrome and death. The four major groups of pathogenic E. coli are enteropathogenic E. coli (EPEC), enteroinvasive E. coli (EIEC), enterotoxigenic E. coli (ETEC), and enterohemorrhagic E. coli (EHEC). EHEC is also known as a Shiga-toxin producing E. coli while the other three are considered by many to be generic or non-Shiga toxin producing E. coli. EPEC Enteropathogenic E. coli is the oldest recognized category of pathogenic E. coli. Pathogenesis of EPEC involves localized adherence of the bacteria to intestinal cells.

This adherence causes an inflammatory response and a physical alteration of the integrity of the intestine. Symptoms of EPEC infection include profuse watery, and sometimes bloody, diarrhea. The only known reservoir for this organism is humans. EPEC are highly infectious for infants and are a leading cause of infantile diarrhea in developing countries. In the sporadic documented cases of adult disease the infectious dose is presumably much higher, at approximately 106 organisms.

Outbreaks have been linked to the consumption of contaminated drinking water and some meat products. EIEC The pathogenic mechanism and disease produced by enteroinvasive E. coli closely resembles that of Shigella. EIEC penetrate and multiply within intestinal cells causing widespread cell destruction and illness. Symptoms include severe abdominal cramps, malaise, watery stools, tenesmus, and fever. Less than 10% of cases develop further illness including the passage of multiple fluid stools containing blood and mucus (dysentery).

The only known reservoir for this organism is humans. Evidence suggests that illness is transmitted by consumption of contaminated food. EIEC infections are endemic in developing countries. The infectious dose of EIEC is thought to be as few as 10 organisms, similar to Shigella, but studies have shown that at least 106 organisms are required to cause illness in healthy adults. ETEC Enterotoxigenic E. coli is an important cause of traveler’s diarrhea in people from industrialized countries who visit developing countries.

It is also an important cause of dehydrating diarrhea in infants and children in developing countries. ETEC are capable of producing a heat-labile enterotoxin (LT - destroyed or altered by heat), a heat-stabile enterotoxin (ST - heat resistant), or both (LT/ST). These organisms invade the small intestine where they proliferate and produce these toxins which induce fluid secretion. Profuse watery diarrhea without blood or mucus, similar to that of a Vibrio cholera infection, usually occurs.

Additional symptoms include abdominal cramps, low-grade fever, nausea, vomiting and malaise. Humans are the major reservoir for ETEC and infection occurs through consumption of contaminated food and water. The infectious dose of ETEC for healthy adults has been estimated to be at least 108 cells. The young, the elderly, and others that are immunocompromised may be susceptible to lower numbers.


Enterohemorrhagic E. coli is a rare variety of E. coli that is considered moderately invasive and produces large quantities of one or more related, potent toxins. These toxins are called verotoxins and Shiga toxins due to their similarity to the toxins produced by Shigella dysenteriae. They cause severe damage to the lining of the intestine making EHEC the primary cause of hemorrhagic colitis. The diarrhea associated with infection may range from mild and non-bloody to stools that are virtually all blood.

Fever is either low-grade or absent and occasional vomiting may occur. Approximately 8% of cases progress to hemolytic uremic syndrome (HUS), which is the most common cause of acute renal failure in children. E. coli O157:H7 is the most well known serotype in the EHEC group; however, there are several other serotypes of importance including O26, O111, O103, O45, and O121. Cattle are the major reservoir for EHEC, but humans may also serve as a reservoir for person-to-person transmission. Infection usually occurs through ingestion of food contaminated with ruminant feces.

Outbreaks has been linked to beef (usually inadequately cooked ground beef), produce (including melons, lettuce, and alfalfa sprouts), and unpasteurized dairy products (milk). Waterborne transmission has also been documented. The infectious dose is very low, probably similar to that of Shigella.

Description of Testing Parameters EHA Routinely Analyze for in our Laboratory Surveillance Program:

EHA strongly believes that a third-party retail food safety audit is not complete without laboratory surveillance. Although testing for pathogens is not necessary unless there are specific indications, testing for Aerobic Plate Count, Enterobacteriaceae and generic E. coli give a very good indication and often shows in a bi-directional manner the results of the actual physical sanitary inspection. In other words, the proof is in the testing. Problems with cleaning and sanitization of food contact surfaces and equipment, temperature abuse, cross-contamination and/or issues with employee hygiene can be picked up with such routine surveillance.

Three to eleven samples are what most EHA clients have submitted for laboratory analysis, which not only tests food that is available for service, but at times, vendors who provide products such as deli meats and leafy greens are also tested. Although most states do not have regulatory standards for food other than milk and other dairy products and, of course, water (ice is considered water), the reference ranges provided below are generally accepted as a level of good sanitation, good food safety and, in fact, are actually regulatory standards in some jurisdictions in the United States.

Aerobic Plate Count (APC) – Reference Range < 100,000 per gram in food; < 20,000 in dairy (per most state regulations and type of dairy product)

Aerobic plate is used as an indicator of the level of bacteria in a product. The APC can be used to evaluate sanitary conditions of a food or water sample. A high APC is an indicator of poor sanitation.

Total Coliform – Reference Range < 100 per gram in food; < 10 – 20 in milk and dairy products (depending on state law); < 10 per 100 ml in potable drinking water

Coliform bacteria are organisms that are present in the environment and in the feces of all warm-blooded animals and humans. Coliform bacteria will not likely cause illness. However, their presence in drinking water and food indicates that disease-causing organisms (pathogens) could be present.

Generic E. coli – Reference Range absent (none) in ready-to-eat foods, dairy and water

Generic E. coli is an indicator of fecal contamination. Fecal contamination is one of the principle sources of pathogenic organisms that contaminate food and water. Fecal contamination in turn indicates that other harmful organisms, whether they be bacterial (Salmonella, Shigella, Campylobacter), viral (hepatitis A, norovirus, rotovirus), helminthic or protozoal parasites (Taenia, Toxoplasma, Cryptosporidium, Giardia), could be present.

Enterobacteriaceae – Reference Range < 100 per gram in food

Enterobacteriaceae is a large family of bacteria which included many enteric pathogens such as Salmonella and E. coli. High counts of Enterobacteriaceae are an indicator of unsanitary conditions in the food processing and preparation environment.

Salmonella – Reference Range absent (none)

Salmonella is a genus consisting of many species of gram negative bacteria, most of which are motile, and are present in animal reservoirs and in the environment. Members of the Salmonella genus cause a variety of diseases such as enteric fever, gastroenteritis, and septicemia. Reactive arthritis involving swelling, pain and inflammation of the joints, is a complication following salmonella enteritidis. Salmonella has also been implicated in cases of osteomyelitis in children with co-existant sickle cell anemia.

Staphylococcus – Reference Range < 100 per gram

Staphylococcus aureus is a gram positive bacterium that usually appears under the microscope as spherical (coccus) organisms appearing in pairs, short chains, or bunched, grape-like clusters. Staphylococcus aureus has been implicated as a causative agent in acute food poisoning episodes, toxic shock syndrome, impetigo, scalded skin syndrome, cellulitis, folliculitis and furuncles. Staphylococcus aureus can cause illness by preformed toxin production as well as by infecting both local tissues and the systemic circulation. Staphylococcus aureus causes acute episodes of food poisoning via preformed enterotoxins.

Food items likely to be infected by staphylococcal food poisoning include meat and meat products; poultry and egg products; salads such as egg, tuna, chicken, potato, and macaroni; bakery products such as cream-filled pastries, cream pies, and chocolate éclairs; sandwich fillings; and milk and dairy products. Incubation Period for foodborne Staphylococcal aureus disease is 1-6 hours. Diagnosis Staphylococcal aureus gastrointestinal illness can be diagnosed by isolating the preformed toxins from the contaminated food item.