Bacteria Classification

Bacteria are classified by shape. Most bacteria have one of three shapes: Cocci; these are cylindrical, they look like little balls

Bacillius; These are “rod shaped”

And Spirilla; these are spiral shaped.

Sometimes you can have intermediate shapes that are described by a combination of the three. For example: coccobacilli (rod shaped but mostly round)

Other terms Prosthecae: starlike appearance Staphylococci: looks like a bunch of grapes. Flagellum: A hair that is whip-like and attached to the bacteria in some way. Most of the time these are used for mobility.

Staining also helps to classify bacteria Gram stain Developed by Danish Physician Dr. Hans Christian Gram in 1884 Procedure: Cells are heated, crystal violet is applied, then iodine is added, then alcohol, then red dye. Gram positive cells: These cells retain the purple dye and mask the red. Gram negative cells: These cells appear red.

What does it mean? Different bacteria have a different composition in their cell walls, therefore you can classify the bacteria by how they stain based on their cell wall composition.

Examples Pneumonia- stain Gram positive Staphylococcus aureus stain Gram positive Escherichia coli stain Gram negative

Acid Fast Staining This procedure is taking a red dye which is applied while the bacteria is being heated, then a fast acting acid is added to decolorize the cells. Only a few cells will retain their red color under these conditions because they have a specific lipid in their cell wall. (Mycolic acid)

Most acid-fast bacteria are of the genus Mycobacterium Examples of diseases that Mycobacteium cause are: tuberculosis and leprosy. Note: These bacteria do not stain well with the Gram stains so acid-fast stains need to be used.

Other ways to classify bacteria By their DNA or RNA (Genetic information) By their metabolism or how they regulate their basic functions. (nutritional requirements, oxygen requirements, temperature and pH) We will get into Metabolism and Genetics later.