If you go online and search up photos of different bacteria species you might be surprised to see mostly pink and purple bacteria. What is up with that?
Bacteria are not naturally these colors or at least many species are not naturally these colors (some can be). Most of the time bacteria on a slide are really difficult to see even with a microscope, so stains have been added to improve contrast.
One of the common staining methods is Gram staining. The process is extremely simple to do, and relatively quick!
First things first, to stain something you need to have something. Scientists take a small amount of distilled water and bacteria on a thin piece of glass called a "slide". This slide is left to dry, and is then heat set to prevent the bacteria from slipping off.
From there they follow these steps:
Apply crystal violet which is purple
Wash off the excess
Apply iodine to help it stick
Wash the iodine off
Ethanol to wash it really good
Wash off the ethanol
Apply safranin which is pink
And finally wash that off.
Once all that is done the slide can be observed! If nothing is visible there's the chance the ethanol was left on for too long, as it can only be left on for 10 seconds or until the purple dye stops dripping off the slide.
When bacteria are Gram stained they will be one of two colors, purple or pink. Pink bacteria are gram negative, while purple ones are gram positive. These two possible types help scientists determine the potential species of a bacteria and other traits it has.
Gram positive bacteria, such as Bacillus anthracis (seen above), have peptidoglycans in their cell walls. They also have thicker cell walls. This means that the first stain, a purple stain, stays in the bacteria after all the washing.
Gram negative bacteria, such as Escherichia coli (seen above), may have peptidoglycans in their cell walls or they may not. If they do have peptidoglycans in their cell walls, the walls are thin and so the peptidoglycans get washed away as well as the purple dye. They are dyed with a pink stain after the washing step so they will be visible.
We should consider ourselves lucky to live in a world where we have the tools to see bacteria, and one where making them into pretty colors helps us know so much more about them.
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