Coccus

Staphylococcus bacteria

A coccus (plural cocci) is any bacterium that has a spherical, ovoid, or generally round shape.^[1] It is one of the three distinct bacterial shapes, the other two being bacillus (rod-shaped) and spiral-shaped cells.

Cocci is an English loanword of a modern or neo-Latin noun, which in turn stems from the Greek masculine noun kokkos (κόκκος) meaning "berry".^[2]

Arrangements

Cocci may occur as single cells or remain attached following cell division. Those that remain attached can be classified based on cellular arrangement:^[1]

Diplococci are pairs of cocci (e.g. Streptococcus pneumoniae and Neisseria gonorrhoeae)
Streptococci are chains of cocci (e.g. Streptococcus pyogenes).
Staphylococci are irregular (grape-like) clusters of cocci (e.g. Staphylococcus aureus).
Tetrads are 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.

References

1 2 Pommerville, J.C. (2013). Fundamentals of Microbiology (10th ed.). Sudbury, MA: Jones & Bartlett. p. 106. ISBN 9781449647964.
↑ κόκκος. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project

Microbiology: Bacteria

Medical
microbiology

Biochemistry
and ecology

Oxygen preference	Aerobic Obligate Anaerobic Facultative Obligate Microaerophile Nanaerobe Aerotolerant
Other	Microbial metabolism Primary nutritional groups Nitrogen fixation Microbial ecology Human flora Gut Lung Mouth Skin Vaginal (In pregnancy) Placental Uterine Salivary Substrate preference Lipophilic Saccharophilic

Shape

Structure

Cell envelope	Cell membrane Cell wall: Peptidoglycan NAM NAG DAP Gram-positive bacteria only: Teichoic acid Lipoteichoic acid Endospore Gram-negative bacteria only: Bacterial outer membrane Porin Lipopolysaccharide Periplasmic space Mycobacteria only: Arabinogalactan Mycolic acid
Outside envelope	Bacterial capsule Slime layer S-layer Glycocalyx Pilus Fimbria Non-motile bacteria
Composite	Biofilm

Taxonomy

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