Peptostreptococcus species


Anaerobic Gram-positive cocci
Peptostreptococcus species


  •  Anaerobic, Gram-positive, non-spore forming bacteria.
  • Cells are small, spherical, and can occur in short chains, in pairs or individually.
  • Peptostreptococcus are slow-growing bacteria with increasing resistance to antimicrobial drugs.
  • Most frequently identified species of Peptostreptococcus is P. magnus.
  • Peptostreptococcus species are commensal organisms in humans, living predominantly in the mouth, skin, gastrointestinal, vagina and urinary tracts, and compose a portion of the bacterial gut flora.
  • Under immunosuppressed or traumatic conditions these organisms can become pathogenic, as well as septicemic, harming their host.
  • Peptostreptococcus can cause brain, liver, breast, and lung abscesses, as well as generalized necrotizing soft tissue infections.
  • Anaerobic gram-positive cocci such as Peptostreptococcus are the second most frequently recovered anaerobes and account for approximately one quarter of anaerobic isolates found.

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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.

  1. Amoxicillin Usual: 250-500 mg orally three times daily or 500-875mg bid.
  2. Augmentin 875/125 mg orally twice daily or  500/125mg three times daily or 1000mg XR (2 tabs=2000mg) q12h   OR  Ampicillin-sulbactam (Unasyn®) 1.5 – 3.0 grams IV q6h
  3. Penicillin VK 500mg orally every 6 hours  OR  Penicillin G 1-2 million units IV q6h
  4. Several others but considered ‘overkill’  e.g. Piperacillin-Tazobactam, Vancomycin, Imipenem, Daptomycin, Linezolid.


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