Bacteria

A domain consisting of prokaryotic organisms. Bacterial characteristics include the ability to adhere to and invade host cells, being toxic and being able to avoid the hosts immune system. Bacteria that cause disease are pathogens.

Bacteria were one of the first life forms on earth, and even though they are microscopically small, of only a few micrometres in length, they are very good at adapting to their environment around them, leading them to inhabit most habitats on Earth. There are many different names for bacteria depending on where they inhabit, such as Physcrophile, Mesophile, Thermophile, Hyperthermophile. 

Bacteria can also be classified on whether they are gram positive or gram negative, which is dictated by their cell wall composition. This can be tested by performing a gram strain procedure.

Gram-Positive bacteria

The cell wall of Gram-Positive bacteria consists of a multilayer of murein, a special type of peptidoglycan, which is significantly thicker compared to Gram-Negative peptidoglycan layer. The cell membrane is located right underneath the peptidoglycan sheets. Additionally, there are molecules called teichoic acids which are situated perpendicularly along the peptidoglycan layers and can be found exclusively in Gram- Positive cell walls. Due to the composition of their cell wall, Gram-Positive bacteria possess the ability to retain crystal violet dye, found in gram stain, and thus appear purple/blue after being washed with alcohol and water.

Gram Negative Bacteria

These bacterial cells have a thin layer of peptidoglycan in their cell wall and stain red after the gram staining procedure.