Are all bacteria harmful?
You may not like the idea, but bacteria are all around us: in our bodies, on our skin, everywhere! Despite the popular idea that all bacteria are out to get us and that we must use every antibacterial soap and antibiotic in the world to combat them, the vast majority of bacteria are actually either harmless or beneficial to our health! Take food products such as natural yoghurt: they have bacteria which help our gut function at its best. It’s all about the balance of the different bacterial types and where the bacteria are located: if they are in the correct place in the body, they are helpful: it’s only when they end up elsewhere that they can potentially be a problem.
Here’s a Youtube clip to help understand bacteria: Understanding Bacteria.
Are bacteria considered as prokaryotic or eukaryotic cells?
Bacteria are considered as prokaryotic cells: instead of a nucleus, their genetic code is laid out either within a nucleoid or as a chromosome (of DNA). They also do not have most of the organelles that most eukaryotes have: you can learn more about eukaryotes in Introduction to Normal Cell Structure. The only organelles that tend to exist within bacteria are the ribosomes. There are also additional organelles that may exist within bacteria: they are known as flagella. They serve the same function as tails on sperm: they help the bacteria to move around.
Why do I mention Gram stain results in Bacterial Infections?
I mention Gram stain results in Bacterial Infections for two reasons:
- Gram staining is the first thing a microbiologist does when they receive a bodily sample in a lab. What this stain does is it reveals the external structure of the bacteria. This is done in conjunction with cultures on agar plates in order to diagnose the the genus/species of bacteria causing a problem. The picture alongside demonstrates both Gram positive (purple) bacteria and Gram negative (pink) bacteria in the same sample.
- The Gram stain results often give a hint as to where the bacteria are located within the body. Gram positive bacteria are usually located on the external surface of the body, such as the skin, whereas Gram negative bacteria are usually located in the gut. There are exceptions on either side of the scale, however.
What do Gram positive and Gram negative bacterial walls look like, and how do they compare to one another?
Gram positive and Gram negative bacterial walls look quite different from one another. I’ll discuss each of them separately.
Gram positive cell walls have two separate layers: the cytoplasmic membrane and the peptidoglycan layer, which is what attracts the crystal violet in the Gram stain. Peptidoglycan is made up of different derivatives of sugar as well as amino acids. The peptidoglycan layer is very thick because it composed of many layers. There are also wall-associated proteins that stick out from this layer: these are referred as teichoic acids. These acids provide the negative charge which makes the crystal violet stick during the washing process.
Unlike Gram positive bacteria, the peptidoglycan layer here is very thin. What makes up for this loss in volume is the thickness of the outer membrane, which is a lipopolysaccharide layer or LPS layer. A lipopolysaccharide layer is made up of both fat and carbohydrates such as glycogen or starch bonded together.
Can the Gram stain be used for all bacteria?
No. One classic example of a bacteria that the Gram stain will not illuminate is Mycobacterium tuberculosis, which causes TB. This requires special staining due to the bacteria’s waxy coat. If TB is suspected in a clinical sample, the Ziehl-Nielson stain (an acid-fast stain) is used: this helps penetrate the waxy layer.
What shapes of bacteria are there?
There are six distinctive shapes of bacteria, but only three of them tend to be seen commonly within microbiology samples seen in a hospital lab. The shapes are as follows:
- Coccus (circle)
- Rod (oval)
- Spirochete (squiggly)
- Spiriullum (spiral)
- Budding and appendaged bacteria
- Filamentous bacteria
Only the first three I mentioned tend to be seen within a hospital lab: I’ll talk about them more extensively in Types of Bacteria.