The type form of bacteria shown in the photograph above is Tetrad.
- A coccus (plural cocci) is any bacterium that has a spherical, ovoid, or generally round shape.
- It is one of the three distinct bacterial shapes, the other two being bacillus (rod-shaped) and spiral-shaped cells.
- Cocci may occur as single cells or remain attached following cell division.
Those that remain attached can be classified based on cellular arrangement:
- Pairs:Diplococci are pairs of cocci (e.g. Streptococcus pneumoniae and Neisseria gonorrhoeae)
- Chains:Streptococci are chains of cocci (e.g. Streptococcus pyogenes).
- Clusters:Staphylococci are irregular (grape-like) clusters of cocci (e.g. Staphylococcus aureus).
- Tetrads :Clusters of four cocci arranged within the same plane (e.g. Micrococcus sp.).
- Sarcina: is a genus of bacteria that are found in cuboidal arrangements of eight cocci.