Streptococcus agalactiae

Streptococcus agalactiae

Background:

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.

Therapy:

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)