The E. coli bacterium lives everywhere in the environment, though it is particularly common in animals. In people, E. coli live in parts of our body that are exposed to the environment, such as our intestines and respiratory tract. In our intestines, the bacteria often live at peace with us and in fact help us by being sources of vitamins K and B complex.
There are hundreds of strains of E. coli. They are classified and numbered by the antigens that they produce. Some of them have acquired genes, either through mutation or from other organisms, that allow them to produce chemicals that are harmful to people. If we ingest these harmful strains, like 0157:H7, they can make us sick by producing these powerful chemical poisons, or toxins. However, most E. coli strains are harmless and live in the intestines of healthy humans and animals.
E. coli is often used by researchers as a basic research tool because it grows quickly. Researchers study its functions and how it reproduces to learn more about bacteria in general, and it is used as a model organism because its behavior is similar to other disease-causing bacteria.
When people eat E. coli-infected food or come directly into contact with E. coli-infected fecal matter, the E. coli bacteria enter the body and make their way to the stomach and small intestine, and often attach to the inside surface of the large intestine. Toxins, or poisons the bacteria secrete, cause swelling of the intestinal wall, which is what causes severe gastrointestinal distress.
E. coli 0157:H7 causes a disease called hemorrhagic colitis, which is the sudden onset of stomach pain and severe cramps. This is followed by diarrhea that is watery and bloody. Sometimes there is vomiting, but there is no fever. The incubation period is three to nine days. The illness lasts about a week, and there are usually no long-term problems.
Antibiotics have little if any effect on this disease and most people recover in 5 to 10 days. There is no specific therapy, but it's important to drink lots of water to stay hydrated, and to eat properly.
HUS is the most common cause of kidney failure in children.
A small percentage of people with E. coli infections get a more serious condition, called hemolytic uremic syndrome (HUS), that can be life-threatening. It develops when the bacteria gets into the circulatory system through the inflamed bowel and releases certain toxins into the blood.
HUS takes one to two weeks to develop, and 50 percent of the people in the United States who come down with the illness die from it. Half of all people who get HUS need dialysis for the rest of their lives, and many infected individuals need blood transfusions.
E. coli is diagnosed through laboratory analysis of a stool sample.
Contaminated meat looks and smells like normal meat, so thorough cooking of food is necessary to prevent disease. Ground meat is more of a risk than whole cuts because in the former the bacteria are mixed in the grinding process and may not be completely killed by cooking, whereas in the latter they are located only on the surface and are more easily killed.
E. coli lives in the intestines of cattle, chicken, deer, sheep, and pigs. Animals are just carriers—E. coli doesn't make them sick. The use of untreated animal manure as fertilizer is a common route of transmission for the bacterium.
E. coli can be spread by eating ground beef, unpasteurized juice or milk, alfalfa sprouts, or water. Person-to-person transmission can occur in places like day care centers, hospitals, and nursing homes, or anywhere people come into contact with fecal matter of an infected individual.
Unlike many infectious organisms, where it takes thousands or tens of thousands of organisms to cause disease, it only takes a few organisms, fewer than 200, for an E. coli infection to occur.
The biggest risk for E. coli infection is eating undercooked beef. Beef should always be thoroughly cooked before eating. Other ways to prevent the ingestion of E. coli include …