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Escherichia or E. coli: Cell Facts, Gut Bacteria, and Infection


A Surprising Bacterium

While you were in school, you may have learned that Escherichia coli living in our large intestine is a helpful bacterium with many benefits. On the other hand, you've probably also heard reports describing dangerous cases of foodborne illness caused by the microbe, which may sometimes be fatal. How can the bacterium be both beneficial and harmful?

The reason for the conflicting reports is that there are many different types of E. coli, which are known as strains. While the strains are similar enough to be given the same species name, there are important differences between them. These differences enable some strains to co-exist with us inside our intestine and others to be dangerous if they enter the body.

E.coli lives in the colon, which is the longest part of the large intestine.


Cells of Escherichia coli

Esherichia coli was officially discovered in 1885 by Theodor Escherich, a German pediatrician. He discovered the microbe in the feces of healthy babies. He called the new organism Bacterium coli because it was a bacterium that lived in the colon (the longest part of the large intestine).

E. coli exists as a microscopic, rod-shaped cell. The cells of most strains of the bacterium are motile and have thin, whip-like extensions on their surface called flagella. The extensions create a beating motion that moves the microbes through their liquid environment. Flagella are most obvious under certain viewing conditions. Since they are attached at several places on the surface of a cell, the bacteria sometimes tumble as they swim.

The bacteria stop swimming when necessary and develop numerous fimbriae. Like flagella, fimbriae extend from the cell surface. They are shorter and thinner than flagella, however. Bacteria use their fimbriae to attach to other bacteria or to the surfaces of objects.

One site of E. coli attachment is the mucus lining the interior of our large intestine. Here the bacterium absorbs nutrients from its surroundings in order to survive. In laboratories, it does well using glucose as a food source. The microbe is a facultative anaerobe—that is, it can survive with or without oxygen.

E. coli Swimming and Tumbling

Quorum Sensing in Bacteria

The Nature of Quorum Sensing

Researchers are discovering that despite their tiny size bacteria are more complex than was previously realized. Studying individual Escherichia coli cells is useful, but studying a group of the bacteria is important as well. New behavior sometimes appears when the microbes are in a group.

When bacteria (including E. coli) are in a dense group, a phenomenon called quorum sensing may develop. During this process, the bacteria coordinate their behavior and respond to a stimulus in the same way and at the same time.

The Role of Autoinducers

Quorum sensing can take place because bacteria communicate with each other via chemicals known as autoinducers. Scientists have found that when the autoinducers in the environment reach a specific concentration—which happens when the population is sufficiently dense—the bacteria in the area detect the high concentration of chemicals and then perform the same behavior. The behavior involves a change in gene expression, or the activity of a gene.

Effects of Quorum Sensing

Quorum sensing may help bacteria to infect their host more efficiently. If researchers can learn more about the process, they may be able to interfere with it and reduce the severity of bacterial infections. That would be a wonderful outcome of the research.

We might be able to use quorum sensing to help us in some way. For example, a group of bacteria could be genetically engineered (genetically modified in some way) so that they all perform a useful action at the same time. One possibility is that they could be used as a sensor to indicate the presence of an activity that is hard for us to detect. E. coli is one species of bacteria that is being engineered for this purpose.

E.coli Swarming

Intestinal Flora and Gut Bacteria

Escherichia coli is a normal component of the intestinal flora. The microbe community in the intestine is also known as the gut flora and the intestinal microbiome. The bacteria in the community are often collectively known as gut bacteria.

The intestinal flora mainly consists of the bacteria, yeasts, and protozoa that live in our large intestine. The intestine is thought to contain trillions of individual microbe cells, most of them bacteria. We may contain more bacterial cells than human ones. This is possible because bacterial cells are generally smaller than ours and because the organisms live in body cavities, such as the intestine.

E.coli isn't the most numerous bacterium in our large intestine, but it does seem to be consistently present. In fact, its presence in the environment is used as an indicator of fecal pollution. One specific benefit of the bacterium is that it makes vitamin K, which we absorb. We need this vitamin in order for our blood to clot when we're wounded. The organism also makes some B-complex vitamins.

Natural, refrigerated sauerkraut contains probiotics. These potentially helpful bacteria and yeasts may become part of the intestinal flora.


Benefits of the Intestinal Microbiome

Researchers are finding that many members of our intestinal flora are beneficial for our health. They make substances that our bodies absorb and use, help to digest food, and interfere with the growth of harmful bacteria. Some have additional benefits, such as helping our immune systems to work better. Investigating the ways in which gut bacteria affect the body is a very active area of scientific research.

Adding useful bacteria to the large intestine may be beneficial. This is the idea behind the use of probiotic supplements and the addition of probiotics to foods and drinks. "Probiotics" are microbes that are thought to support our lives.

Some exciting evidence shows the importance of a healthy microbiome in the large intestine. In some serious and debilitating cases of a Clostridium difficile gut infection, the medical administration of a fecal transplant has been very helpful. The feces is obtained from someone who is healthy and has a normal collection of intestinal flora. The normal bacteria multiply in the recipient's intestine and overcome the effects of the harmful one.

Genetic Engineering in E. coli

E. coli in Biotechnology

E. coli affects our lives in another way besides its intestinal benefits. It's a popular organism in biotechnology labs, where scientists use the bacterium to study the process of combining genes from different cells and organisms. The goal of the scientists is to better understand how genes work and to develop techniques that will benefit humans in some way.

One example of genetic engineering involving E. coli cells is their use in insulin production. Scientists have incorporated the human gene that directs the manufacture of insulin into the DNA (deoxyribonucleic acid) of E. coli. DNA is the genetic material in bacteria and in us. Insulin is an essential hormone in our bodies but isn't normally made by bacteria. The genetically altered bacteria make insulin, which is given to people with Type 1 diabetes. People with this condition are unable to make their own hormone.

Produce is healthy and delicious, but it needs to be washed if it's eaten raw in order to remove bacteria and reduce the chance of foodborne illness.


E. coli Infection

E. coli lives in the intestines of both humans and animals. A person can become infected by pathogenic strains of the bacterium by eating contaminated food or drinks or after touching feces— even a very small amount—that has come from an infected person or animal. Pathogenic bacteria can cause disease.

One type of food that may contain dangerous strains of the microbe is undercooked beef. Bacteria in the cow's intestine can be transferred to the meat during the butchering process. Raw vegetables, sprouts, and fruits can be contaminated if they come into contact with animal manure or contaminated water. Raw milk products, raw nuts, and unpasteurized fruit juices may also cause foodborne illness produced by E. coli cells.

Raw vegetables and fruits need to be washed well to prevent a bacterial infection.


Possible Symptoms of an Infection

Possible symptoms of an E. coli infection include stomach cramps, nausea, vomiting, and diarrhea, which may be bloody. Some people get no symptoms from the infection. In other people, the infection may cause a few days of discomfort and then disappear. It may sometimes be serious, however, and even deadly. Symptoms generally appear after an incubation period of several days.

The people who are most likely to suffer severe effects from the bacterial infection are those that are very old or very young or people with weakened immune systems. Anyone with diarrhea that doesn't quickly disappear or is bloody should visit a doctor, however. This advice is also important for someone who has severe vomiting or a high fever.

Cantaloupes may have potentially dangerous  bacteria on their surface.

Cantaloupes may have potentially dangerous bacteria on their surface.

Pathogenic Strains of the Bacterium

Pathogenic E. coli strains can affect the intestine, the urinary tract, the respiratory tract or, in the case of newborn babies, the meninges (the three membranes that surround the brain). The most common site of infection is the large intestine, however.

The bacteria have features that help them to infect an area and stay there so that they can't be removed. For example, some strains make adhesins, structures on the cell membrane that help them stick to surfaces. Some produce invasins, proteins which enable the bacteria to enter human cells. Others produce toxins, chemicals that harm the host in some way.

Scientists are finding that although all E. coli are classified in the same species, there is actually a considerable amount of variability in their genes and in the molecules on their surfaces. A number of labeling systems have been developed to identify the different strains. For example, E. coli 0157:H7 is a strain that causes disease, E. coli K-12 is a strain that's used in laboratory experiments, and UPEC E. coli (Uropathogenic Escherichia coli) causes urinary tract infections. A special classification system is sometimes used for strains of E. coli that produce diarrhea, as shown in the table below.

Strains of Escherichia coli That Cause Diarrhea

Diffusedly Adherent E.coli, or DAEC, also seems to cause diarrhea, although it is less easy to characterize than the above strains.

TypeAbbreviationAction in the IntestineSymptoms

Enterotoxigenic E. coli


Attaches to the intestine by fimbriae and produces a toxin

Traveler's diarrhea (or Montezuma's revenge), with no fever

Enteroinvasive E. coli


Enters and destroys cells lining the colon

Watery diarrhea with fever

Enteropathogenic E. coli


Attaches to the intestinal lining via a protein called intimin

Watery diarrhea, which may be bloody

Enteroaggregative E. coli


Forms clumps on the lining of the intestine and produces a toxin

Diarrhea, which may be prolonged

Enterohemorrhagic E. coli (or Shiga Toxin-Producing E. coli)


Attaches via intimin and produces Shiga toxin

Bloody diarrhea, possible kidney damage

An E. coli cell with fimbriae, which help it attach to the intestinal lining


Preventing Bacterial Infections

Some simple safety procedures will greatly reduce the chance of an E. coli infection.

  • Cook meat to a safe temperature. Use a digital thermometer to monitor the temperature instead of a mercury one. The latter kind is dangerous if it releases mercury.
  • Keep raw meat separate from other foods.
  • Wash your hands before and after preparing food.
  • Wash countertops and utensils thoroughly after food preparation.
  • Wash and scrub raw vegetables and fruits before eating, paying particular attention to peels with crevices, such as the rind of cantaloupes. Bacteria can pass into the flesh of a cantaloupe as it's cut.
  • Drink and eat only pasteurized fruit juices and dairy products
  • Drink from a safe water supply
  • Wash your hands after contact with animals.
  • Follow good hygiene techniques in high-risk areas, such as public restrooms and bathrooms.

Although it's important to protect ourselves from pathogenic E. coli, it's good to know that some strains of the bacterium are beneficial. Bacteria can be helpful as well as harmful.


  • Bacterial Quorum Sensing: Its Role in Virulence and Possibilities for Its Control (Abstract) from Cold Spring Harbor Perspectives in Medicine
  • Repurposing E. coli by Engineering Quorum Sensing from Intechopen
  • Difference between foodborne illness and food poisoning from the USDA
  • Escherichia coli facts and news from the CDC (Centers for Disease Control and Prevention), including information about the latest outbreaks of foodborne illness caused by the bacterium
  • Information about an E. coli infection from the NIH (National Institutes of Health)
  • Fecal transplant for a Clostridium difficile infection from John Hopkins Medicine


© 2012 Linda Crampton


Linda Crampton (author) from British Columbia, Canada on February 13, 2015:

Thank you very much, Mkala.

Mkala on February 13, 2015:

Thanks a lot for your information on E.coli, and I think is beneficial to me & others scientists.


Thanks for the visit and the vote, Dianna. You've raised a very good point - an E. coli infection and other disorders that cause gastrointestinal symptoms can sometimes be confused.

Dianna Mendez on October 21, 2012:

What a great hub post and one that comes in really handy as we head towards the flu season. Sometimes what seems like flu can be contamination from E coli. Great advice on how to prevent this as well. Seems like keeping things disinfected is the best prevention. Voted up.


Thank you for the comment and the vote, Mommy Needs a Nap. It's nice to meet you!


Thank you very much, drbj. I appreciate the great comment and the vote!!

Michelle Clairday from Arkansas on October 21, 2012:

Very interesting and well researched. Voted up.

drbj and sherry from south Florida on October 21, 2012:

What a thorough examination of the E-coli bacterium, Alicia. Take a bow, m'dear, because your explanation is far easier to understand than any medical text I have ever read. Trust me. Voted up therefore! And the videos are a bonus.


Thanks for commenting and for the support, Tom. As always, I appreciate your votes and the share!

Thomas Silvia from Massachusetts on October 21, 2012:

Hi my friend, great well written and researched hub, i did not know some of this. Thanks so much for helping me learn more about this subject .

Vote up and more !!! SHARING !

Linda Crampton (author) from British Columbia, Canada on October 20, 2012:

Thank you very much for the comment and the vote, Mary! E. coli are fascinating bacteria, and they're very important creatures. Some strains are extremely useful, but it's sad that other strains can be very harmful.

Mary Hyatt from Florida on October 20, 2012:

Wow! You did a great job researching this topic, and your Hub is very informative and useful.

It is also a good educational Hub, too. I learned things about these bacteria that I never knew.

I voted this Hub UP, etc.


Thanks for the comment and the information, Kris. It sounds like you have a very interesting job! Cloning and genetic engineering are fascinating topics. I would have liked to have gone into more detail about these topics, but I'll save that for a future hub - this one is long enough!

Kris Heeter from Indiana on October 20, 2012:

You've done an nice job of touching on a lot of facts about E. coli. In research labs, it is one of the most commonly used bacterial strains used to shuttle, store and replicate DNA from various organisms, including humans, as you touched on. I oversee an archival facility that hosts over 1.5 million DNA "clones" - these clones are basically E. coli that carry genes or parts of genes from other organisms. Upon request from other scientists, we can grow up a clones to make more copies and ship it off to distant labs for further research.