What is the recommended treatment for Heavy Streptococcus anginosus, an abnormal Beta (Beta-hemolytic) Streptococcus non-Group A isolate?

Treatment of Heavy Streptococcus anginosus (Beta-Hemolytic Non-Group A)

For heavy Streptococcus anginosus infections, initiate penicillin G 12-18 million units/day IV divided in 4-6 doses for 4 weeks, combined with mandatory surgical drainage of any abscesses, as antibiotics alone are insufficient for abscess-forming infections. 1, 2

Initial Assessment and Empiric Coverage

Before culture confirmation, if the patient presents with systemic toxicity or severe invasive infection:

• Start broad-spectrum empiric therapy with vancomycin or linezolid PLUS piperacillin-tazobactam or a carbapenem, as S. anginosus frequently causes abscess formation and may be accompanied by anaerobes or other pathogens 2
• Obtain at least 2 sets of blood cultures every 24-48 hours until bloodstream infection clears 1
• Obtain infectious diseases consultation at the time of antimicrobial therapy initiation 1

Definitive Antimicrobial Therapy

Once S. anginosus is confirmed:

Standard regimen (penicillin-susceptible, MIC ≤0.125 mg/L):

• Penicillin G 12-18 million units/day IV in 4-6 divided doses for 4 weeks 1, 2
• Alternative: Amoxicillin 100-200 mg/kg/day IV in 4-6 doses for 4 weeks 1, 2
• Alternative: Ceftriaxone 2 g/day IV or IM once daily for 4 weeks 1, 2

Critical distinction from other streptococci: Short-term 2-week therapy is NOT recommended for S. anginosus, unlike other oral streptococci, due to its propensity for abscess formation 1

Add gentamicin 3 mg/kg/day IV in 1 dose for the first 2 weeks to enhance bacterial killing, particularly in severe infections 1

Penicillin-Allergic Patients

• Vancomycin 30 mg/kg/day IV in 2 equally divided doses for 4 weeks 1
• When vancomycin is used, gentamicin addition is NOT needed 1

Surgical Management - MANDATORY

The most critical pitfall is relying solely on antibiotics without adequate surgical drainage, which is the most common cause of treatment failure. 2

• Surgical drainage is absolutely mandatory and should not be delayed 2
• S. anginosus produces abscesses in cardiac tissue, visceral organs, and may cause myocardial abscesses, septic arthritis, and vertebral osteomyelitis 1
• Clinical reassessment within 48-72 hours is essential to ensure appropriate response 2

Special Clinical Scenarios

Endocarditis (Native Valve):

• Penicillin G 12-18 million units/day IV for 4 weeks PLUS gentamicin 3 mg/kg/day for 2 weeks 1
• Group B streptococci and S. anginosus may require adjunctive surgery due to abscess formation 1

Prosthetic Valve Endocarditis:

• Mortality is very high, and cardiac surgery is strongly recommended 1, 2
• Extend therapy to 6 weeks 1

Necrotizing Fasciitis or Toxic Shock Syndrome:

• Penicillin G PLUS clindamycin 600-900 mg IV every 8 hours 2
• Clindamycin suppresses toxin production and maintains efficacy at high bacterial loads 2
• Urgent surgical debridement is mandatory and must not be delayed 2

Resistance Considerations

• While S. anginosus is generally susceptible to penicillin, some strains may display variable penicillin resistance 1, 3
• Rare strains with altered penicillin-binding proteins may show resistance to third-generation cephalosporins despite negative penicillin screening 4
• For severe infections, determine aminopenicillin and third-generation cephalosporin susceptibility directly rather than relying solely on penicillin screening 4
• Resistance to erythromycin (5.7%) and clindamycin has emerged in some regions 5

Monitoring and Follow-Up

• Count duration of antimicrobial therapy beginning on the first day blood cultures are negative 1
• If operative tissue cultures are positive, administer an entire antimicrobial course after valve surgery 1
• Investigate for underlying conditions, as S. anginosus bacteremia is associated with malignancies (particularly colon cancer), dental infections, and gastrointestinal disease 2

Critical Pitfalls to Avoid

• Never rely solely on antibiotics without adequate surgical drainage - this is the most common cause of treatment failure 2
• Avoid inadequate duration of therapy, especially for deep-seated abscesses, as premature discontinuation leads to relapse 2
• Do not use 2-week short-course therapy for S. anginosus, even if penicillin-susceptible, unlike other oral streptococci 1
• Do not delay surgical intervention while waiting for antimicrobial response 2