coccus

Spherical bacterium. Many species have characteristic arrangements that are useful in identification. Pairs of cocci are called diplococci; rows or chains, streptococci (see streptococcus); grapelike clusters, staphylococci (see staphylococcus); packets of eight or more cells, sarcinae; and groups of four cells in a square arrangement, tetrads. These characteristic groupings occur as a result of variations in the reproduction process.

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Cocci (singular - coccus, from the Latin coccinus (scarlet) and derived from the Greek kokkos (berry) ) are any microorganism (usually bacteria) whose overall shape is spherical or nearly spherical. Describing a bacterium as a coccus, or sphere, distinguishes it from bacillus, or rod. This is the first of many taxonomic traits for identifying and classifying a bacterium according to binomial nomenclature.

Aggregations

Aggregations of coccoid bacteria often occur and these forms have specific names as well; listed here are the basic forms as well as representative bacterial genera:

• pairs, or diplococci (Neisseria)
• groups of four or eight known as tetrads or sarcina (Micrococci)
• bead-like chains, or streptococci (Streptococcus)
• grapelike clusters, or staphylococci (Staphylococcus)

Clinical significance

Important human pathogens caused by coccoid bacteria include staphylococci infections, some types of food poisoning, some urinary tract infections, toxic shock syndrome, gonorrhea, as well as some forms of meningitis, throat infections, pneumonias, and sinusitis.

References

External links

• Bacteria Picture Gallery