E. coli

E. coli is a bacterium, meaning a tiny single-celled organism. Its full name is Escherichia coli, named after the pediatrician Theodor Escherich, who discovered it in 1885. It lives in the gut of humans and many animals, usually completely harmlessly. A single specimen is about two thousandths of a millimeter long and can only be seen under a microscope. Under good conditions it divides every 20 minutes, so a single cell becomes billions overnight. It is precisely this speed that has made E. coli the most important workhorse of biology.

From gut dweller to the standard tool of biology

Anyone who wants to understand life needs a system that is fast, cheap, and consistent everywhere. E. coli meets all three conditions. A lab can start an experiment and read the result the next morning. With mice or plants, the same thing would take weeks or months.

That is why many fundamental rules of life were first discovered in this bacterium. This includes how cells read their genetic information and translate it into proteins. Because the same rules also apply to human cells, this knowledge was far more than mere bacteriology. Several Nobel Prizes trace back to work done with E. coli.

It’s important to make a distinction: E. coli is not automatically a pathogen. There are thousands of variants, called strains. Most are harmless, and some laboratory strains are deliberately weakened so that they barely survive outside their nutrient broth. Only a few strains, such as EHEC, actually cause illness.

How the bacterium is converted into a protein factory

Every cell has a blueprint, the DNA. It contains, in a kind of chemical script, instructions for which proteins the cell should produce. Proteins are the tools of life, for example the hormone insulin. The cell reads the blueprint and assembles the protein piece by piece.

In E. coli, an additional piece can be inserted into this blueprint. Small ring-shaped pieces of DNA are used for this, which the bacterium voluntarily takes up. If the ring carries the blueprint for human insulin, the bacterium subsequently produces insulin. It doesn’t notice that the protein isn’t naturally its own, and simply keeps working.

You can picture this like a copier with a foreign template inserted. The copier doesn’t check what’s on the page, it just duplicates it. The bacteria are then grown in large steel tanks, often several thousand liters. In the end, the desired protein is filtered out of the broth and purified.

Insulin, hygiene tests, and food recalls

The best-known application is insulin for people with diabetes. It used to be obtained from pig pancreases; since 1982 it has come from reprogrammed bacteria. Enzymes for detergents and components of vaccines are also produced this way. In business news, such processes appear under the term biotechnology.

In everyday life, the name is most often encountered in warning notices. Because E. coli comes from the gut, its detection in drinking water or salad is considered a sign of fecal contamination. Authorities therefore regularly test lakes and waterworks for this bacterium. If it is found, closures or recalls follow, often before anyone even gets sick.

A common misconception is that E. coli is generally dangerous. In fact, here it mainly serves as an indicator, much like a warning light. It doesn’t show the harm itself, but reveals that more dangerous germs could have taken the same path. Dangerous strains such as EHEC produce toxins and can cause severe diarrhea, but they are the exception.