Bacteria are a very diverse group of organisms! Here we will learn about one of many characteristics that can help you distinguish between your bacteria samples in the lab.
Bacteria are usually categorized by the presence or absence of a thick layer of peptidoglycan in their cell walls. Some bacteria have just a thin layer of peptidoglycan in their cell wall, and directly around it will be an outer membrane. Other bacteria will lack that outer membrane but will have multiple thick layers of peptidoglycan.
To determine whether the bacteria have this layer, a lab technique is used known as the Gram stain test. To briefly summarize, this test involves staining the bacteria using crystal violet. Peptidoglycan will retain the purple color from crystal violet, so if by the end of your test your bacteria show up as purple under the microscope, then you have gram-positive bacteria. This means that your bacteria do have that thick layer of peptidoglycan. In contrast, gram-negative bacteria do not have that layer, so they will not show up as purple.
During this test, there is a step involving using ethanol as a decolorizer. This is crucial in determining whether your bacteria are gram-positive or negative because the ethanol will be able to wash away the crystal violet stain from the bacteria if their cell walls have a thin peptidoglycan layer. In other words, if they are gram-negative. What you will then see under the microscope are pink bacteria, because of the safranin stain that is also used in this test.
Below I have included a video detailing the process of how to do a Gram stain test!
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