What treats Streptococcus agalactiae infections?

Treatment of Streptococcus agalactiae Infections

Penicillin G remains the first-line antibiotic for treating Streptococcus agalactiae (Group B Streptococcus, GBS) infections, with ampicillin as an acceptable alternative, and these agents maintain universal susceptibility without documented resistance. 1, 2, 3

Perinatal/Neonatal Context: Intrapartum Prophylaxis

For prevention of early-onset neonatal GBS disease in colonized pregnant women:

• Penicillin G 5 million units IV initial dose, then 2.5 million units IV every 4 hours until delivery is the preferred regimen due to its narrow spectrum 1
• Ampicillin 2 g IV initial dose, then 1 g IV every 4 hours until delivery is an acceptable alternative 1

Penicillin-Allergic Patients (Intrapartum)

The approach depends on anaphylaxis risk 1:

Low risk for anaphylaxis (no history of immediate hypersensitivity, anaphylaxis, angioedema, urticaria, or asthma):

• Cefazolin 2 g IV initial dose, then 1 g IV every 8 hours until delivery 1

High risk for anaphylaxis (history of immediate hypersensitivity reactions):

• If susceptibility testing shows clindamycin and erythromycin susceptibility: Clindamycin 900 mg IV every 8 hours OR erythromycin 500 mg IV every 6 hours until delivery 1
• If susceptibility unknown or resistance present: Vancomycin 1 g IV every 12 hours until delivery 1, 4

Invasive GBS Disease in Neonates

For confirmed neonatal sepsis or meningitis 2:

• Penicillin G 250,000-300,000 units/kg/day divided every 4 hours for meningitis (7-14 days depending on organism) 2
• Penicillin G 150,000-300,000 units/kg/day divided every 4-6 hours for pneumonia/endocarditis 2
• Maximum daily dose should not exceed 12-20 million units 2

Invasive GBS Disease in Adults

For serious infections including bacteremia, endocarditis, and soft tissue infections 2:

• Penicillin G 12-24 million units/day by continuous IV infusion or divided doses 2
• Duration depends on infection type: 2-6 weeks for endocarditis, 10-14 days for bacteremia 2

Alternative Agents for Penicillin-Allergic Adults

• Vancomycin 15-20 mg/kg IV every 8-12 hours (adjust for renal function, target trough 15-20 mcg/mL for serious infections) 4
• Cefazolin 1-2 g IV every 8 hours for non-anaphylactic penicillin allergy 1

Necrotizing Soft Tissue Infections

When GBS causes necrotizing fasciitis or streptococcal toxic shock syndrome 1:

• Penicillin 2-4 million units IV every 4-6 hours PLUS clindamycin 600-900 mg IV every 8 hours 1
• Clindamycin is critical for toxin suppression and superior efficacy demonstrated in animal models and observational studies 1
• Surgical debridement is mandatory and takes precedence over antibiotics 1
• Continue antibiotics until no further debridement needed, clinical improvement achieved, and afebrile for 48-72 hours 1

Healthcare Worker Carriage Eradication

For pharyngeal carriage 1:

• Penicillin V 500 mg PO four times daily for 10 days OR amoxicillin 500 mg PO three times daily for 10 days 1
• If penicillin fails: Clindamycin 300 mg PO four times daily for 10 days 1

For non-pharyngeal carriage 1:

• Clindamycin 300 mg PO four times daily for 10 days OR azithromycin 500 mg PO daily for 5 days 1
• Penicillin alone is insufficient for non-pharyngeal sites 1

Critical Considerations and Pitfalls

Antibiotic resistance patterns 3, 5, 6:

• GBS remains universally susceptible to penicillin with no documented resistance 1, 3
• Increasing resistance to clindamycin, erythromycin, and fluoroquinolones has been observed 3, 5
• High-level gentamicin resistance (HLGR) is emerging in specific hypervirulent serotype IV strains, which abrogates synergistic therapy 6
• Rare vancomycin resistance has been reported 3

Duration of therapy 2:

• Minimum 10 days for streptococcal infections to prevent rheumatic complications (though this primarily applies to Group A streptococci, the principle of adequate duration applies) 1
• Continue treatment 48-72 hours after patient becomes asymptomatic for most acute infections 2

Synergy considerations 4:

• Vancomycin combined with aminoglycosides acts synergistically against GBS in vitro 4
• However, HLGR strains negate aminoglycoside synergy, making this combination unreliable in areas with emerging resistance 6

Prevention remains paramount 7:

• Intrapartum antibiotic prophylaxis has successfully reduced early-onset disease but has not impacted late-onset neonatal disease rates 7, 3
• Conjugate vaccines targeting serotypes Ia, Ib, II, III, and V are under development and may provide more comprehensive prevention 7