Coccus A
coccus (plural
cocci, from the Latin
coccinus (scarlet) and derived from the Greek
kokkos (berry)), is any
microorganism (usually
bacteria) whose overall shape is
spherical or nearly spherical. Coccus refers to the shape of the bacteria and can contain multiple genera, such as staphylococci or streptococci. Cocci can grow in pairs, chains, or clusters, depending on their orientation and attachment during cell division. In contrast to many bacilli-shaped bacteria, most cocci bacteria do not have flagella and are non-motile. Cocci is an English
loanword of a
modern or Neo-Latin noun, which in turn stems from the
Greek masculine noun () meaning 'berry'. Important human diseases caused by coccoid bacteria include
staphylococcal 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.
Arrangements Coccoid bacteria often occur in characteristic arrangements and these forms have specific names as well; listed here are the basic forms as well as representative bacterial
genera: The various gram-positive cocci differ physiologically and by habitat.
Micrococcus spp. are obligate aerobes that inhabit human skin.
Staphylococcus spp. also inhabit human skin, but they are facultative anaerobes. They ferment sugars, producing lactic acid as an end product. Many of these species produce carotenoid pigments, which color their colonies yellow or orange.
Staphylococcus aureus is a major human pathogen. It can infect almost any tissue in the body, frequently the skin. It often causes nosocomial (hospital-acquired) infections. Presumably, diplococcus has been implicated in
encephalitis lethargica. The genus
Neisseria belongs to the family Neisseriaceae. This genus,
Neisseria, is divided into more than ten different species, but most of them are gram negative and coccoid. The gram-negative, coccoid species include:
Neisseria cinerea,
N. gonorrhoeae,
N. polysaccharea,
N. lactamica,
N. meningitidis,
N. mucosa,
N. oralis and
N. subflava. The most common of these species are the pathogenic
N. meningitidis and
N. gonorrhoeae. The genus
Moraxella belongs to the family
Moraxellaceae. This genus,
Moraxellaceae, comprises gram-negative coccobacilli bacteria:
Moraxella lacunata,
M. atlantae,
M. boevrei,
M. bovis,
M. canis,
M. caprae,
M. caviae,
M. cuniculi,
M. equi,
M. lincolnii,
M. nonliquefaciens,
M. osloensis,
M. ovis,
M. saccharolytica, and
M. pluranimalium. However, only one has a morphology of diplococcus,
M. catarrhalis, a salient pathogen contributing to infections in the human body. The species
Streptococcus pneumoniae belongs to the genus
Streptococcus and the family
Streptococcaceae. The genus
Streptococcus has around 129 species and 23 subspecies that benefit many microbiomes on the human body. There are many species that show non-pathogenic characteristics; however, there are some, like
S. pneumoniae, that exhibit pathogenic characteristics in the human body. These gram-positive, coccoid bacteria were once thought to be harmless to the human body. However, within the last ten years, there has been an influx of nosocomial pathogens originating from
Enterococcus bacteria. Bacilli usually divide in the same plane and are solitary, but can combine to form diplobacilli, streptobacilli, and palisades. • Diplobacilli: Two bacilli arranged side by side with each other. • Streptobacilli: Bacilli arranged in chains. • Coccobacillus: Oval and similar to coccus (circular shaped bacterium). There is no connection between the shape of a bacterium and its color upon
Gram staining; there are both gram-positive rods and gram-negative rods.
MacConkey agar can be used to distinguish among gram-negative bacilli such as
E. coli and
salmonella.
Arrangements Bacilli usually divide in the same plane and are solitary, but can combine to form diplobacilli, streptobacilli, and palisades. • Diplobacilli: Two bacilli arranged side by side with each other. • Streptobacilli: Bacilli arranged in chains. The word
coccobacillus reflects an intermediate shape between
coccus (spherical) and
bacillus (elongated).
Coxiella burnetii is also a coccobacillus. Bacteria from the genus
Brucella are medically important coccobacilli that cause
brucellosis.
Haemophilus ducreyi, another medically important Gram-negative coccobacillus, is observed in sexually transmitted disease, chancroid, of Third World countries.
Spiral Spiral bacteria are another major bacterial cell morphology. Spiral bacteria can be sub-classified as spirilla, spirochetes, or vibrios based on the number of twists per cell, cell thickness, cell flexibility, and motility.
Bacteria are known to evolve specific traits to survive in their ideal environment. Bacteria-caused illnesses hinge on the bacteria's physiology and their ability to interact with their environment, including the ability to
shapeshift. Researchers discovered a protein that allows the bacterium
Vibrio cholerae to morph into a corkscrew shape that likely helps it twist into — and then escape — the protective mucus that lines the inside of the gut. Examples include: •
Leptospira species, which cause
leptospirosis. •
Borrelia species, such as
Borrelia burgdorferi, a tick-borne bacterium that causes
Lyme disease •
Treponema species, such as
Treponema pallidum, subspecies of which causes
treponematoses, including
syphilis Helical Helicobacter species are
helically shaped, the most common example of which is
Helicobacter pylori. A helical shape is seen to be better suited for movement of bacteria in a viscous medium. == See also ==