Dictionary > Streptococcus agalactiae

Streptococcus agalactiae

A gram-positive, beta-hemolytic, catalase-negative coccus that may form chains, and belonging to the family Streptococcaceae
Streptococcus agalactiae is a gram-positive coccus (spherical in shape). It belongs to the genus Streptococcus wherein its members are classified according to their hemolytic properties. Some Streptococcus species are alpha-hemolytic that can cause oxidation of iron in hemoglobin. Others are beta-hemolytic. Beta-hemolytic species are capable of rupturing erythrocytes completely and therefore distinctively produce clear areas around their bacterial colonies on blood agar. Others still are gamma-hemolytic. Streptococcus agalactiae is a beta-hemolytic. It is also facultative anaerobe. Apart from this classification, there is a so-called Lancefield grouping (which is a serotype classification). Accordingly, there are groups A to V based on the twenty serotypes identified. Streptococcus agalactiae has a bacterial capsule composed of exopolysaccharide and belongs to the Lancefield group B. As such, the species is referred to as group B streptococcus. Since there are further serotypes (i.e. (Ia, Ib, II–IX) depending on the immunologic reactivity to the polysaccharide capsule, the species is also referred to as group B streptococci (plural form, referring to the serotypes).
The species is generally a harmless commensal (normal flora) in human gastrointestinal and genitourinary tract. However, its growth may lead to disease, such as non-gonococcal urethritis (or gonorrhea).
Also called:

  • group B streptococcus (GBS)

Scientific classification:

  • Domain: Bacteria
  • Phylum: Firmicutes
  • Class: Coccus
  • Order: Lactobacillales
  • Family: Streptococcaceae
  • Genus: Streptococcus
  • Species: S. agalactiae
  • See also:

    User Contributions / Comments:

    contributed by J. McGlorie on 7 April 2007 (MDT)