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A coccus (plural cocci, from the Latin coccinus (scarlet) and derived from the Greek kokkos (berry)), is any microorganism (usually bacteria) [1] whose overall shape is spherical or nearly spherical. [2] [3] [4] Coccus refers to the shape of the bacteria and can contain multiple genera, such as staphylococci or streptococci. Cocci can grow in ...
[31] [32] [33] Bacteria may alter their shape by simpler transitions from rod to coccoid (and vice versa) as in Escherichia coli, [34] by more complex transitions while establishing multicellularity [31] or by the development of specialized cells, structures or appendages where the population presents a pleomorphic lifestyle. [35]
Bacterial morphological plasticity refers to changes in the shape and size that bacterial cells undergo when they encounter stressful environments. Although bacteria have evolved complex molecular strategies to maintain their shape, many are able to alter their shape as a survival strategy in response to protist predators, antibiotics, the immune response, and other threats.
Cell shape is generally characteristic of a given bacterial species, but can vary depending on growth conditions. Some bacteria have complex life cycles involving the production of stalks and appendages (e.g. Caulobacter) and some produce elaborate structures bearing reproductive spores (e.g. Myxococcus, Streptomyces).
Streptococcus is a genus of gram-positive or spherical bacteria that belongs to the family Streptococcaceae, within the order Lactobacillales (lactic acid bacteria), in the phylum Bacillota. [2] Cell division in streptococci occurs along a single axis , thus when growing they tend to form pairs or chains, which may appear bent or twisted.
This causes the bacteria to form filaments, elongated cells that lack internal cross-walls. [10] After a period of time, the cell walls of the filaments are digested, and the bacteria collapse into very large spheres surrounded by just their cytoplasmic and outer membranes.
The genera Corynebacterium [9] and Coccobacillus [10] have been designated as a pleomorphic genera, diphtheroid Bacilli have been classified as pleomorphic nosocomial bacteria. [11] Additionally, in one study focused on agents involved in a non-infectious disease, pleomorphic bacteria were found to exist in the blood of healthy human subjects. [12]
Some bacteria, called vibrio, are shaped like slightly curved rods or comma-shaped; others can be spiral-shaped, called spirilla, or tightly coiled, called spirochaetes. A small number of other unusual shapes have been described, such as star-shaped bacteria. [44]