Dictionary:
strep·to·coc·cus (strĕp'tə-kŏk'əs)
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streptococcus |
Britannica Concise Encyclopedia:
streptococcus |
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Sci-Tech Encyclopedia:
Streptococcus |
A large genus of spherical or ovoid bacteria that are characteristically arranged in pairs or in chains resembling strings of beads. Many of the streptococci that constitute part of the normal flora of the mouth, throat, intestine, and skin are harmless commensal forms; other streptococci are highly pathogenic. The cells are gram-positive and can grow either anaerobically or aerobically, although they cannot utilize oxygen for metabolic reactions. Glucose and other carbohydrates serve as sources of carbon and energy for growth. All members of the genus lack the enzyme catalase. Streptococci can be isolated from humans and other animals.
Streptococcus pyogenes is well known for its participation in many serious infections. It is a common cause of throat infection, which may be followed by more serious complications such as rheumatic fever, glomerulonephritis, and scarlet fever. Other beta-hemolytic streptococci participate in similar types of infection, but they are usually not associated with rheumatic fever and glomerulonephritis. Group B streptococci, which are usually beta-hemolytic, cause serious infections in newborns (such as meningitis) as well as in adults. Among the alpha-hemolytic and nonhemolytic streptococci, S. pneumoniae is an important cause of pneumonia and other respiratory infections. Vaccines that protect against infection by the most prevalent capsular serotypes are available. The viridans streptococci comprise a number of species commonly isolated from the mouth and throat. Although normally of low virulence, these streptococci are capable of causing serious infections (endocarditis, abcesses). See also Pneumonia.
Columbia Encyclopedia:
streptococcus |
Types of Streptococci
Streptococci are classified into the alpha, beta, or gamma groups, according to their action on blood cells. Streptococci of the alpha group (e.g., the viridans and S. pneumoniae) cause some destruction (hemolysis) of red blood cells. The beta group are more destructive of red blood cells; they also produce toxic substances that affect white blood cells and the clotting properties of blood. Members of these two groups are sometimes called hemolytic (red blood cell-destroying) streptococci. The beta-hemolytic streptococci are often further classified into lettered groups, called Lancefield groups for R. C. Lancefield, the scientist who originated the scheme in the 1930s. Group A hemolytic streptococci are responsible for most human streptococcal disease; group B hemolytic streptococci can cause serious problems in newborns. The gamma group, or nonhemolytic group, does not affect red blood cells. Enterococci (usually harmless bacteria that inhabit the intestines) and lactococci (bacteria used in starter cultures in the production of fermented dairy products) used to be considered a part of the Streptococcus genus but are now placed in their own genera.
S. pneumoniae and Viridans Infections
The viridans are normal inhabitants of the body and are usually harmless; however, they can contribute to tooth decay. Streptococcus pneumoniae is the most common cause of otitis media in children. It can also cause meningitis and pneumonia. The S. pneumoniae diseases are sometimes referred to as pneumococcal diseases. The development of drug-resistant strains of pneumococci has caused concern in the medical community. Vaccination against pneumococcal pneumonia is recommended for very young children and older persons; the vaccine inoculates against the most prevalent strains of S. pneumoniae.
Group A Streptococcal Infections
Group A hemolytic streptococci cause over a dozen diseases, including some pneumonias, erysipelas (a generalized body infection), upper respiratory infections, wound infections, and puerperal fever. Scarlet fever is also a streptococcal, or strep, infection; the rash is a response to a toxin produced by the bacteria that cause strep throat. Rheumatic fever follows an initial Group A streptococcal infection: proteins of the streptococcal cells stimulate antibody formation by the body (see immunity), and these antistreptococcal antibodies are believed to react with and damage many tissues of the body, especially heart muscle. Kidney disease (acute glomerulonephritis) is another complication of streptococcal infections. Some extremely serious Group A streptococcal infections began to emerge or reemerge in the late 1980s. Toxic streptococcal syndrome was first described in 1987. It is a rapidly progressing infection, similar to septicemia, that usually infects people in their 20s or 30s. Necrotizing fasciitis is a quickly spreading infection of the flesh and muscle caused by toxins released by a strain of Group A streptococcal bacteria that have been invaded by bacteriophages. Such bacteria are popularly called "flesh-eating bacteria."
Group B Streptococcal Infections
Group B streptococci are a common cause of infection in babies, pregnant women, the elderly, and immunologically compromised adults. They are especially serious in newborns, in whom they can cause sepsis, meningitis, or pneumonia. Group B streptococci are often present in people who show no symptoms of disease; these people are said to be "colonized." Many infants are colonized before or during birth by mothers who unknowingly carry the bacteria. A small percentage of these develop disease, which can be life-threatening or can lead to lifelong neurological problems.
Bibliography
See M. P. Starr et al., ed., The Prokaryotes: A Handbook on Habitats, Isolation and Identification of Bacteria (1981).
Health Dictionary:
streptococcus |
A category of bacteria that can cause various infections in humans, including scarlet fever and strep throat.
Veterinary Dictionary:
streptococci |
Bacterial members of the genus Streptococcus.
Wikipedia:
Streptococcus |
| Streptococcus | |
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| Scientific classification | |
| Kingdom: | Bacteria |
| Phylum: | Firmicutes |
| Class: | Bacilli |
| Order: | Lactobacillales |
| Family: | Streptococcaceae |
| Genus: | Streptococcus Rosenbach, 1884 |
| Species | |
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S. agalactiae |
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Streptococcus is a genus of spherical Gram-positive bacteria belonging to the phylum Firmicutes[1] and the lactic acid bacteria group. Cellular division occurs along a single axis in these bacteria, and thus they grow in chains or pairs, hence the name — from Greek στρεπτος streptos, meaning easily bent or twisted, like a chain (twisted chain). Contrast this with staphylococci, which divide along multiple axes and generate grape-like clusters of cells. Streptococci are oxidase- and catalase-negative, and many are facultative anaerobes.
In 1984, many organisms formerly considered Streptococcus were separated out into Enterococci and Lactococci.[2]
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Contents
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In addition to streptococcal pharyngitis (or strep throat), certain Streptococcus species are responsible for many cases of meningitis, bacterial pneumonia, endocarditis, erysipelas and necrotizing fasciitis (the 'flesh-eating' bacterial infections). However, many streptococcal species are non-pathogenic. Indeed, Streptococci are a necessary ingredient in Emmentaler ("Swiss") cheese. Streptococci are also part of the normal commensal flora of the mouth, skin, intestine, and upper respiratory tract of humans.
As a rule, individual species of Streptococcus are classified based on their hemolytic properties. [3] Alpha hemolysis is caused by a reduction of iron in hemoglobin, giving it a greenish color on blood agar. Beta-only hemolysis is complete rupture of red blood cells, giving distinct, wide, clear areas around bacterial colonies on blood agar. Other streptococci are labeled as gamma hemolytic, actually a misnomer, as no hemolysis takes place.
Beta-hemolytic streptococci are further characterised via the Lancefield serotyping – based on specific carbohydrates in the bacterial cell wall.[4] These are named Lancefield groups A to v(except I and J), although some species, such as S. pneumoniae, do not express Lancefield antigens, but these are alpha-hemolytic not the beta-hemolytic to which this scheme refers. In the medical setting, the most important groups are the alpha-hemolytic streptococci, S. pneumoniae and Streptococcus Viridans-group, and the beta-hemolytic streptococci of Lancefield groups A and B (also known as “Group A strep” and “Group B strep”).
S. pyogenes, also known as Group A Streptococcus (GAS), is the causative agent in Group A streptococcal infections, including streptococcal pharyngitis ("strep throat" AmE), acute rheumatic fever, scarlet fever, acute glomerulonephritis and necrotizing fasciitis. If strep throat is not treated, it can develop into rheumatic fever, a disease that affects the joints and heart valves. Other Streptococcus species may also possess the Group A antigen, but human infections by non-S. pyogenes GAS strains (some S. dysgalactiae subsp. equisimilis and S. anginosus Group strains) appear to be uncommon.
Group A Streptococcus infection is generally diagnosed with a Rapid Strep Test (AmE) or by culture.
S. agalactiae, or GBS, causes pneumonia and meningitis in neonates and the elderly, with occasional systemic bacteremia. They can also colonize the intestines and the female reproductive tract, increasing the risk for premature rupture of membranes and transmission to the infant. The American College of Obstetricians and Gynecologists, American Academy of Pediatrics and the Centers for Disease Control recommend all pregnant women between 35 and 37 weeks gestation should be tested for GBS. Women who test positive should be given prophylactic antibiotics during labor, which will usually prevent transmission to the infant.[5] In the UK, clinicians have been slow to implement the same standards as the US, Australia and Canada. In the UK, only 1% of maternity units test for the presence of Group B Streptococcus.[6] Although The Royal College of Obstetricians and Gynaecologists issued risk-based guidelines in 2003 (due for review 2006), the implementation of these guidelines has been patchy. Some groups feel that as a result over 75 infants in the UK die each year of GBS related disease and another 600 or so suffer serious infection, most of which could be prevented [7] however this is yet to be substantiated by randomized controlled trial in the UK setting and, given the evidence for the efficacy of testing and treating from other countries, it may be that the large-scale trial necessary would receive neither funding nor ethics approval.[8]
Includes S. equi, which causes strangles in horses,[9] and S. zooepidemicus - a subspecies of S. equi - which causes infections in several species of mammals including cattle and horses. This can also cause death in chickens and moose.
Many former Group D streptococci have been reclassified and placed in the genus Enterococcus (including S. faecalis, S. faecium, S. durans, and S. avium).[10] For example, Streptococcus faecalis is now Enterococcus faecalis.
The remaining non-enterococcal Group D strains include Streptococcus bovis and Streptococcus equinus.
These streptococci are usually but not exclusively beta hemolytic. Streptococcus canis is an example of a GGS which is typically found on animals but can cause infection in humans.
Non-hemolytic streptococci rarely cause illness. However, weakly hemolytic group D beta-hemolytic streptococci and Listeria monocytogenes should not be confused with non-hemolytic streptococci.
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