Streptococcus agalactiae


>Streptococcus anginosus group (formerly Streptococcus milleri)
     1] Streptococcus intermedius
     2] Streptococcus anginosus
     3] Streptococcus constellatus
>Streptococcus pneumoniae
>Streptobacillus moniliformis
>Streptococcus pyogenes (Groups A, B, C, G, F)
>Streptococcus agalactiae  (Group B streptococcus)Led

Streptococcus agalactiae

  • (also known as Group B streptococcus or GBS).
  • Beta-hemolytic Gram-positive streptococcus.
  • CAMP test:  important test for identification. GBS (group B Streptococcus species) are screened through this test. It is characterized by the presence of group B Lancefield antigen and by its ability to hydrolyze sodium hippurate.
  • Sensitive to bile, and will lyse in its presence.
  • S. agalactiae’s polysaccharide antiphagocytic capsule is its main virulence factor.
  • S. agalactiae is a member of the gastrointestinal normal flora in some humans and can spread to secondary sites – genitourinary tract of women 20-30%. Clinical importance: S. agalactiae can be transferred to a neonate passing through the birth canal and can cause serious group B streptococcal infection.
  • S. agalactiae is the major cause of bacterial septicemia of the newborn, which can lead to death or long-term sequelae. S. agalactiae invades via alveolar and pulmonary epithelial cells; newborns are especially susceptible to infection because they lack alveolar macrophages to prevent invasion.


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Important considerations:  The choice of an agent should be based on local antimicrobial sensitivities, site of infection, cost, and comorbid conditions.   Generally, the most common agents/regimens are listed first.    Listed dosages may need to be adjusted for renal dysfunction.

  1. Penicillin G 2-4 million units IV q4-6h
  2. Ampicillin 2 grams IVPB every 4-6 hours
  3. Clindamycin  600mg IV every 6 or 8 hours or 300mg orally four times daily 
  4. Ceftriaxone 1-2 grams IV q24h
  5. Azithromycin 500mg orally x 1 then 250mg once daily for 4 days
  6. Vancomycin 1 gram  ivpb q12h (patient-specific dosing required)
  7. Penicillin G 2-4 million units IV q4-6h  + gentamicin (e.g. meningitis, endocarditis)

Streptococcus agalactiae