Does Oxacillin Cover Group C Streptococcus?
Yes, oxacillin provides effective coverage for Group C streptococcal infections, as these organisms remain highly susceptible to penicillinase-resistant penicillins like oxacillin.
Antibiotic Susceptibility Evidence
Group C streptococci demonstrate excellent susceptibility to oxacillin and other beta-lactam antibiotics. In a comprehensive susceptibility study of 312 beta-hemolytic streptococcal isolates, only 2 out of 50 Group C strains (4%) showed resistance to oxacillin, while all Group C isolates remained susceptible to third and fourth-generation cephalosporins, imipenem, and vancomycin 1. This resistance rate is minimal and comparable to the near-universal susceptibility seen with Group A streptococci.
Clinical Application
For confirmed Group C streptococcal infections, oxacillin (2 g IV every 6 hours) or nafcillin represents appropriate first-line therapy 2. The IDSA guidelines for skin and soft tissue infections specifically list oxacillin and nafcillin as recommended agents for surgical site infections away from the axilla or perineum, which would include Group C streptococcal infections 2.
Group C streptococci (particularly Streptococcus dysgalactiae subsp. equisimilis) are emerging pathogens that cause infections ranging from pharyngitis and skin/soft tissue infections to invasive disease including bacteremia and toxic shock syndrome 3. Treatment with penicillin or penicillinase-resistant penicillins like oxacillin is adequate under most circumstances 3.
Important Caveats
While oxacillin provides excellent coverage, the FDA label indicates oxacillin is specifically indicated for penicillinase-producing staphylococci 4. However, its spectrum of activity includes streptococci, and it is routinely used for these infections in clinical practice.
Penicillin G remains the preferred agent for Group C streptococcal infections when susceptibility is confirmed, as it has a narrower spectrum and is equally effective 1.
Alternative resistance patterns exist: Group C streptococci show higher resistance rates to tetracyclines (20.2% to tetracycline, 18.3% to doxycycline) and moderate resistance to macrolides (5.8% to erythromycin) 1.
For necrotizing fasciitis or toxic shock syndrome caused by Group C streptococci, combination therapy with penicillin plus clindamycin is recommended (extrapolating from Group A streptococcal guidelines), as clindamycin suppresses toxin production 2.