Cover of FAQ: E. Coli: Good, Bad, and Deadly

If you followed news headlines in the spring/summer of 2011, you may recognize E. coli as the agent responsible for outbreaks of serious diarrheal illness in Germany. But this is only one small part of the story of E. coli; its relationship to human health and the food we eat is much more complex. Not all E. coli are bad—in fact most are not—and some are even beneficial! In this report the larger story of E. coli is told: its role in human health, in food and even in our understanding of our own biology.

What is E. coli, anyway?

E. coli is a bacterium; a one-celled organism that is too small to see by the naked eye, and is also sometimes referred to as a microorganism or microbe. E. coli is an abbreviation of the organism’s full scientific name: Escherichia coli. Scientists normally use E. coli for short; similar to how we call ourselves humans, rather than using our full scientific name Homo sapiens. E. coli got its first name, Escherichia, from the German pediatrician Theodor Escherich, who discovered the bacteria in 1885. Its second name, coli, means "from the colon," which is the organism’s natural habitat. Most E. coli live and grow harmlessly in the gastrointestinal tract, or gut, of many animals, including humans.

There are many different types of E. coli. Scientists refer to these different types as strains. In a sense, E. coli strains are like dog breeds, all strains of E. coli are the same type of organism but they may have somewhat different traits. Like dog breeds, different E. coli strains can mix with each other to produce new strains with a combination of traits. Scientists sort E. coli into different strains according to the particular set of marker compounds they carry on their surfaces (not unlike dogs’ different colors and textures of hair). For example, the E. coli strain responsible for the outbreaks in Germany is named O104:H4. The letter "O" refers to a marker on E. coli’s surface that is found in hundreds of different shapes, in this case, shape #104. The "H" describes a different marker that is found on the E. coli’s flagellum, a tail-like appendage used by E. coli to swim around. It is not the "H" or "O" molecules themselves that make E. coli lethal. They are simply markers that are easy to detect, allowing us to tell 1 E. coli strain from another.

Unfortunately, the E. coli strains people are most familiar with are those that cause disease. Perhaps the most infamous strain is O157:H7, which was responsible for the Jack in the Box hamburger outbreak in 1993 and the more recent spinach outbreak in 2006. Rather than existing harmlessly in our gut, disease-causing strains like O157:H7 disrupt body functions, resulting in diarrhea. The most dangerous strains can also affect the kidneys and nervous systems of victims, causing permanent damage and sometimes even resulting in death.

Yet despite all the attention given to their harmful brethren, most E. coli are not harmful to humans, and some are even beneficial. Many of us host a population of E. coli in our gut that aids digestion and protects us from other harmful microbes. Scientists have used strains of E. coli to study fundamental biological processes, contributing to many important scientific breakthroughs and teaching generations of biology students the rudiments of the scientific method. Other E. coli strains are utilized by researchers in industry to produce important compounds we use every day.

*A special thanks to Diana Vullo who translated the teaching poster into Spanish for us.


Michael Ingerson-Mahar, Ann Reid. 2011. FAQ: E. coli: good, bad, and deadly.

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