beta-hemolytic streptococci

(redirected from R antigen)

β-he·mo·lyt·ic strep·to·coc·ci

those that produce active hemolysins (O and S) that cause a zone of clear hemolysis on the blood agar medium in the area of the colony; β-hemolytic streptococci are divided into groups (A-O) on the basis of cell wall C carbohydrate (see Lancefield classification); Group A (in the strains pathogenic in humans) comprises more than 50 types (designated by Arabic numerals) determined by cell wall M protein, which seems to be associated closely with virulence and is produced chiefly by strains with matt or mucoid colonies, in contrast to nonvirulent, glossy colony-producing strains; other surface protein antigens such as R and T (substance T), and the nucleoprotein fraction (substance P) seem to be of less importance. The more than 20 extracellular substances elaborated by strains of β-hemolytic streptococci include erythrogenic toxin (elaborated only by lysogenic strains), deoxyribonuclease (streptodornase), hemolysins (streptolysins O and S), hyaluronidase, and streptokinase.

beta-hemolytic streptococci

the pyogenic streptococci of groups A, B, C, E, F, G, H, K, L, M, and O that cause hemolysis of red blood cells in blood agar in the laboratory. These organisms cause most of the acute streptococcal infections seen in humans, including scarlet fever, many cases of pneumonia and sepsis syndrome, and streptococcal sore throat. Penicillin is usually prescribed to treat these infections when they are suspected, even before the results of the bacteriological culture are available, because it is known that these organisms as a group are usually sensitive to the effects of penicillin and because the sequelae of untreated streptococcal infection may include glomerulonephritis and rheumatic fever.


(strep?to-kok'us) (-kok'si?) plural.streptococci [ strepto- + coccus]
An organism of the genus Streptococcus. See: bacteria for illus streptococcic, adjective

a-hemolytic streptococci

Streptococci that, when grown on blood-agar, produce a zone of partial hemolysis around each colony and often impart a greenish appearance to the agar. Included are S. pneumoniae and viridans group streptococci.

ß-hemolytic streptococci

group B streptococci

group A streptococci

Beta-hemolytic streptococci (esp. Streptococcus pyogenes) that produce human diseases, including pharyngitis, cellulitis, erysipelas, impetigo, otitis media, pneumonia, scarlet fever, necrotizing fasciitis, sepsis, sinusitis, and tonsillitis. In addition, group A streptococcus infection may have immunologic sequelae such as rheumatic fever and acute glomerulonephritis.

group B streptococci

Streptococci that, when grown on blood-agar, produce complete hemolysis around each colony, indicated by a yellowish zone. Included are S. pyogenes and S. agalactiae.These streptococci are a leading cause of early-onset neonatal infections and late-onset postpartal infections. In women, this is marked by urinary tract infection, chorioamnionitis, postpartum endometritis, bacteremia, and wound infections complicating cesarean section. Eradication of this organism during labor decreases the chances for neonatal sepsis. Performance of cervical-rectal screening cultures at 35 to 37 weeks’ gestation (and intrapartum treatment with penicillin if cultures are positive) prevents the development of neonatal sepsis.
Synonym: ß-hemolytic streptococci

group D streptococci

Any Streptococcus species, including S. bovis and S. equinus, that is not destroyed by bile or exposure to heat. These strains can be destroyed in a laboratory by a 6.5% concentration of sodium chloride. Many Group D streptococci have been reclassified and placed in the genus Enterococcus (including S. faecalis, S. faecium, S. durans, and S. avium). For example S. faecalis is now E. faecalis. The remaining strains of nonenterococcal Group D streptococci include S. bovis and S. equinus.

nutritionally variant streptococcus

Abbreviation: NVS
The obsolete name for bacteria of the genera Abiotrophia or Granulicatella.