#gram stain

[bacteriashowdown]

Gram-positive vs. Gram-negative bacteria

a.k.a. the inspiration for this blog's icon

When researching your favorite species of bacteria, the first characteristic you're guaranteed to find is whether or not your bacteria is gram-positive or gram-negative. This is in reference to the Gram stain, a method of staining bacteria with dye, such that certain bacteria retain it and become purple (gram-positive), while others do not -- and after an alcohol wash, can be tinted pink with a counterstain (gram-negative). This staining procedure is almost always the first step in figuring out what kind of bacteria you're working with, and is used constantly for both clinical and research purposes.

Okay, but why? And why does the color of a dyed bacterium even matter?

The answer to these questions... lies in the structure of the cell wall. Gram-positive bacteria retain dye because their cell walls are much thicker. The typical gram-positive bacteria has one cell membrane, covered by a thick layer of peptidoglycan, which is a polysaccharide that gives structural strength to the cell. In contrast, the typical gram-negative bacteria has two cell membranes, separated by a thin layer of peptidoglycan: this layered structure is thinner and more flexible. Gram-negative bacteria can be counterstained because this outer membrane is porous, and is degraded by the alcohol wash, losing its ability to retain the original dye.

This difference in cell structure may not seem earth-shattering, but it does have some serious implications. For example, in medicine, you want to know if you're dealing with a gram-negative bacteria, because they are less susceptible to antibiotics that target the cell wall (such as penicillin): in essence, the outer membrane protects the cell. Penicillin can easily fit between the gaps in the peptidoglycan layer surrounding gram-positive cells, but not through the outer membrane of gram-negative cells, which selectively blocks the passage of toxic substances. In general, gram-negative bacteria are less vulnerable to environmental toxins.

Gram-positive bacteria have their own strengths. In fact, they have an extremely powerful tool at their disposal: unlike (almost all) gram-negative bacteria, some gram-positive bacteria are capable of forming endospores. Endospore formation is an intense survival mechanism where a bacterium creates a dormant structure inside itself (called an endospore), which is extremely durable but cannot self-replicate. When conditions have improved, the endospore transforms into a bacterium, and begins to metabolize and reproduce. Endospores can lie dormant for thousands -- and some argue, millions -- of years, and remain viable.

To summarize: what at first may seem like a simple question of microbial dye-jobs is actually a way to peer into the structure of a bacteria, and hopefully start to unravel the unique strategies and adaptations that the species employs for survival.

Happy Gram staining everyone!

[er-cryptid]

S. aureus at 40x after Gram staining

[hojarascart]

some staining I did today at the laboratory

[sevgrestuanghr]

Gram stain

[spokenforinvaliduser]

[collgeruledzebra]

fuck control man i can't believe im saying "bingo bango" unironically

[ratcandy]

hate how this stupid website has influenced my vocab so much .i go to lab and mumble to myself shit like "in the lab. straight up 'staining it'. and by 'it,' haha well. let's just say. my grams" like nobody says that. shut up

[dilfsisko]

What’s wrong, babe? You’ve hardly absorbed your crystal violet into your cell wall

[lveholic]

just finished a lab that drained me of everything i think .

[amnenome]

Life of a biology student!! If you’re wondering why I don’t post art more often this is why

[sukimas]

actually maybe i should get a microscope specifically to argue with doctors with.

[beaniebeby]

we should study men under a microscope

[gales-boyfriend]

how does my professor grade so fast omg 😮

[so-emo-i-fell-apart]

I THINK THIS MICRO PROFESSOR IS INSANE

[quartzskies]

every day i work the more rage i have towards specimen processors

[fake-heroine]

funniest thing about house is the concept that these doctors do literally any of the lab tests themselves