Escherichia coli (E. coli) as Indicator of Fecal Contamination

Escherichia coli, E. coli in short, are a large and diverse family of bacteria that usually survive in the small intestine of the human and animal body. First described in 1885,  E. coli has become recognized as both a harmless commensal and a versatile pathogen. Although most types of  E. coli are harmless and live in the intestines (guts) of healthy humans and animals, the O157:H7 type produces a powerful toxin that can cause severe illness. E. coli  gets into the food supply through contamination by tiny (usually invisible) amounts of human or animal feces. Thus E. coli is a frequent cause of food poisoning or food-borne illness.  E. coli can also be transmitted by contaminated hands.  Eating food contaminated with harmful strains of E. coli can cause diarrhea, cramps, nausea, headaches or other symptoms. Many people may develop mild symptoms, but some suffer severe complications that can lead to kidney failure and death. In 2011, an  E. coli  outbreak originating in Germany sickened more than 4,000 people, ultimately killing 50 people in 15 countries. The outbreak was eventually traced to contaminated bean sprouts.

E. coli is not spread by coughing, kissing or normal interactions with friends. E. coli can be transferred to animal udders and then milk.  Therefore, the bacteria can also be found in milk products such as cheese, as the contamination can pass through the udder of the cow. E. coli can also be transferred to farm produce via manure. The transmission of  E. coli  O157:H7 from manure-contaminated soil and irrigation water to lettuce plants has been demonstrated. Viable E. coli cells have been recovered from the inner tissues of plants.  It has also been found that E. coli  O157:H7 migrates to internal locations in plant tissue and is therefore protected from the action of sanitizing agents by virtue of its inaccessibility. Experiments have shown that E. coli  O157:H7 can enter the lettuce plant through the root system and migrate throughout the edible portion of the plant.

E. coli O157:H7 is one of the most serious food-borne pathogens worldwide causing physical effects ranging from diarrhea to hemorrhagic colitis.  Cattle is a major reservoir of E. coli O157:H7, therefore outbreaks are primarily associated with consumption of undercooked ground beef.  Cross-contamination of infected meat with points of contact during processing makes it extremely difficult to contain.

E. coli Testing

E. coli is a member of the fecal coliform group. Coliforms are often referred to as “indicator organisms”. While they are not harmful their presence in the environment can indicate that conditions are favorable for pathogens to be present. Since E. coli is a coliform of fecal origin, its presence in a sample is considered a reliable indicator of the possible presence of other more harmful bacteria and fecal contamination. The Total Coliform/E. coli test is a fast inexpensive way to assess the cleanliness of an environment or food and water and can also be used to glean information regarding the potential for other contamination. Indicator tests such as this are used instead of more specific tests because they are less expensive. Since there are dozens of potential water- and foodborne bacteria that are harmful it becomes prohibitively expensive to test for all dangerous species individually.

When a sample is tested and determined to contain E. coli, the lab then tests the sample to determine what strain of E. coli is present. That helps health officials investigate a common source between different cases.