Streptococcus agalactiae

Streptococcus agalactiae
Scientific classification
Domain: Bacteria
Kingdom: Bacillati
Phylum: Bacillota
Class: Bacilli
Order: Lactobacillales
Family: Streptococcaceae
Genus: Streptococcus
Species:
S. agalactiae
Binomial name
Streptococcus agalactiae
Lehmann and Neumann, 1896

Streptococcus agalactiae (also known as group B streptococcus or GBS) is a gram-positive coccus (round bacterium) with a tendency to form chains (as reflected by the genus name Streptococcus). It is a beta-hemolytic, catalase-negative, and facultative anaerobe.[1][2]

S. agalactiae is the most common human pathogen of streptococci belonging to group B of the Rebecca Lancefield classification of streptococci. GBS are surrounded by a bacterial capsule composed of polysaccharides (exopolysaccharide). The species is subclassified into ten serotypes (Ia, Ib, II–IX) depending on the immunologic reactivity of their polysaccharide capsule.[1][3][4]

The plural term group B streptococci (referring to the serotypes) and the singular term group B streptococcus (referring to the single species) are both commonly used synonymously with S. agalactiae even though S. halichoeri and S. pseudoporcinus are also group B Streptococci. These species test positive as group B, but are not frequently carried by humans, and only rarely cause disease.[5]

In general, GBS is a harmless commensal bacterium being part of the human microbiota colonizing the gastrointestinal and genitourinary tract of up to 30% of healthy human adults (asymptomatic carriers). Nevertheless, GBS can cause severe invasive infections especially in newborns, the elderly, and people with compromised immune systems.[6]

S. agalactiae is also a common veterinary pathogen, because it can cause bovine mastitis (inflammation of the udder) in dairy cows. The species name agalactiae meaning "of no milk", alludes to this.[7]

  1. ^ a b Whiley RA, Hardie JM (2009). Genus I. Streptococcus Rosenbach 1884. Bergey's Manual of Systematic Bacteriology: Vol 3: The Firmicutes (2nd ed.). Springer. pp. 655–711. ISBN 978-0-387-95041-9.
  2. ^ Ryan KJ, Ray CG, et al., eds. (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill. pp. 286–8. ISBN 978-0-8385-8529-0.
  3. ^ Edwards MS, Nizet V (2011). Group B streptococcal infections. Infectious Diseases of the Fetus and Newborn Infant (7th ed.). Elsevier. pp. 419–469. ISBN 978-0-443-06839-3.
  4. ^ Slotved HC, Kong F, Lambertsen L, Sauer S, Gilbert GL (2007). "Serotype IX, a proposed new Streptococcus agalactiae serotype". J Clin Microbiol. 45 (9): 2929–2936. doi:10.1128/jcm.00117-07. PMC 2045254. PMID 17634306.
  5. ^ "Guidelines for the Detection and Identification of Group B Streptococcus" (PDF). The American Society for Microbiology. July 23, 2021.
  6. ^ Cite error: The named reference Edwards-Baker-Mandell was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference Keefe1997 was invoked but never defined (see the help page).
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