Pink or Purple?

Small but Deadly

Bacteria are small prokaryotic cells that play a big role in our lives. Most live on us harmlessly and the ones that make us sick aren’t doing it out of spite, they just want out of our bodies. In order to successfully treat bacterial infections, we must kill the bacteria; yet before we can kill them, we must first identify them. There are many ways to do this, but the easiest method is to perform a gram stain.

Gram Who?

The first rule in biology is: if there is a rule, there will always be an exception to that rule (except this one, see what I mean?). While about 90% of all bacteria have cell walls that can be classified as Gram positive (Gram+) or Gram negative (Gram-), there are outliers that either don’t have a cell wall or don’t stain. This post is addressing the 90%, not the exceptions.

A gram stain of mostly Gram+ bacteria

Cell Walls

You can imagine the cell wall as a wooden container with a balloon inside of it. Sharp objects, hot objects, a curious porcupine, a snappy chihuahua, or overinflation can all pop the balloon. The cell wall protects the cell from these incidences of potential popping because popping leads to cell death. Like any container, different materials make up the cell wall of different bacteria.

Gram+ cells are made out of a protein sugar mixture called peptidoglycan and stain purple.
Gram- cells are made out of a combination of fats and carbohydrates called lipopolysaccharide and they stain pink.

The More You Know

Knowing if a certain type of bacteria is Gram+ or Gram- can give doctors a better idea of what antibiotics or treatments will work best. Different treatments target different types of cell walls, either puncturing them, breaking them, or seeping in to poison the cell. The end goal of all these treatments is to kill the cell (pop the balloon). As the Chinese philosopher Sun Tzu once said,

“If you know the enemy and know yourself, you need not fear the result of a hundred battles. If you know yourself but not the enemy, for every victory gained you will also suffer a defeat. If you know neither the enemy nor yourself, you will succumb in every battle.”

Now, Sun Tzu was not talking about bacteria and fighting disease, but knowing your enemy and your bacteria cell wall type is a good place to start.

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