E. Coli: How It Is Identified

When we are usually discussing how we test for specific pathogens and bacteria, many people are often left wondering what exactly we mean when we say that. Of course, we know what they are looking for in these tests (the pathogens, obviously).

E. Coli

But how do we get that result in the first place? It’s not like it comes up on a printed piece of paper with a given sample, so there have to be signs that scientists and researchers can follow, right?

How do they know when they are dealing with a sample of E. Coli bacteria, for example?

Well, that’s what we are going to demonstrate here in this short piece! We are going to explain some of the characteristics that the bacteria E. Coli has, that allow researchers to identify it when they are looking for it through scientific means.

Tests For Bacteria

Generally speaking, when scientists are looking for the presence of bacteria in something, they will usually allow a sample that they want to test to interact with some kind of medium, such as a prepared agar test.

The result, how the medium is affected by a sample, will often help scientists or researchers determine what kind of bacteria can cause these effects, and help narrow down what bacteria are present in the sample they used.

And, being a bacterium, E. Coli has plenty of effects that can be measured!

Gram Staining Test Result

The gram staging test is a laboratory test that is commonly used by scientists to determine what the cause of bacterial infection might be the cause for an infection in a given sample.

When a sample is placed under a gram stain, the bacteria in question will usually change to a certain color, either blue, purple, red, or pink.

From this result, a scientist will be able to broadly identify if a bacteria is present in the sample, being considered gram-positive if it turns blue or purple, and being gram-negative if it turns the stain red or pink.

In the case of E. coli, the result is gram-negative, so the presence of it will turn your stain pinkish or red.

Shape Of The Bacteria

When placed under a powerful light microscope, a person will notice have certain bacteria have specific shapes to them. Scientists and researchers have divided these shapes into 5 broad groups:

  • Cocci bacteria are usually spherical.
  • Bacilli bacteria, which will appear to look like a rod.
  • Spirilla bacteria are usually in some type of spiral.
  • Vibrios, resemble a comma under enough magnification.
  • Spirochaete bacteria, that will look like a corkscrew shape

Being a bacilli-type bacteria shape, E. Coli will look like a short rod when observed under a microscope.


This is a simple measurement, and researchers usually use it to distinguish between bacteria that use the energy created from metabolic processes to move, or can only be moved through an external force affecting it.

E. Coli does have the ability to move under its energy, so would be considered motile.

Flagella Type

Similar to motility, this effectively describes if the bacteria that is being tested has any flagella, the very thin, ropy, almost thread-like, appendages that are viewable under a microscope to move around.

E. Coli is a bacterium that has flagella that it uses to move, so is considered flagellated.


This is a test that is carried out by researchers to determine whether a bacterium is considered aerobic, or anaerobic, by measuring the breakdown and release of oxygen and water from hydrogen peroxide, created by the enzyme catalase.

A positive result would show the production of bubbles in a solution, whereas a negative would show few if any bubbles being released.

E. Coli does have the enzyme catalase in its system, so it would show up as positive.

Final Thoughts

As you can see, there are plenty of tests that can be carried out to determine if a sample has E. Coli and can be identified. There are many more out there, so be sure to learn as much as you can about E. Coli!

Jennifer Dawkins

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