streptococcus (strĕp'təkŏk`əs), any of a group of gram-positive bacteria, genus Streptococcus, some of which cause
disease. Streptococci are spherical and divide by fission, but they remain attached and so grow in beadlike chains. The
incidence and severity of streptococcal diseases decreased dramatically after the introduction of
antibiotics. Antibiotic,
any of a variety of substances, usually obtained from microorganisms, that inhibit the growth of or destroy certain other
.....  (penicillin, erythromycin, and selected cephalosporins are all effective against the organisms),
but the medical
community was shaken by the arrival in the
late 1980s of several severe forms of streptococcal infection
and by the emergence of several drug-resistant strains
(see drug resistance. drug resistance, condition in
which infecting bacteria can resist the destructive effects of drugs such as antibiotics and sulfa drugs .

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

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.

Group A Streptococcal Infections
Group A hemolytic streptococci cause over a dozen diseases, including some pneumonias, erysipelas erysipelas
(a generalized body infection), upper respiratory infections, wound infections, and puerperal fever. Scarlet fever scarlet
fever or scarlatina
, an acute, communicable infection, caused by group A hemolytic streptococcal bacteria (see
streptococcus ) that
.....   is also a streptococcal, or strep, infection; the rash is a response to a
toxin toxin, poison produced by living
organisms. Toxins are classified as either exotoxins or endotoxins.
..... produced by the bacteria that cause strep throat.
Rheumatic fever rheumatic fever
...  follows an initial Group A streptococcal infection: proteins of the streptococcal cells stimulate antibody formation by
the body (see
immunity immunity, ability of an organism to resist disease by identifying and destroying foreign
substances or organisms.
...., 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 bacteriophage
..... . 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.

See M. P. Starr et al., ed., The Prokaryotes: A Handbook on Habitats, Isolation and Identification of Bacteria (1981).

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