In a patient with cellulitis and a wound culture that grows Staphylococcus aureus and rare Enterococcus faecalis, should both organisms be treated?

Treatment of Cellulitis with S. aureus and Rare E. faecalis Growth

You should treat the Staphylococcus aureus and NOT routinely treat the rare Enterococcus faecalis growth in typical cellulitis cases. The rare growth of enterococcus likely represents colonization or contamination rather than a true pathogen requiring treatment.

Rationale Based on Guidelines

The IDSA guidelines for skin and soft tissue infections provide clear direction that cellulitis is predominantly caused by β-hemolytic streptococci, with S. aureus playing a secondary role 1. Importantly, the guidelines explicitly state that cultures of cutaneous aspirates, biopsies, or swabs are not routinely recommended for typical cellulitis 1, which underscores the limited clinical utility of wound cultures in this setting.

Why Enterococcus Should Not Be Treated

Enterococcus faecalis is not a recognized pathogen in typical cellulitis. The guidelines make no mention of enterococcus as a causative organism in cellulitis 1, 2. When wound cultures grow multiple organisms, the clinical question becomes: which organism is causing disease versus which is colonizing the wound surface?

Key considerations:

• "Rare growth" suggests low bacterial burden, making pathogenicity even less likely
• Enterococcus is a common skin and GI tract colonizer that frequently contaminates wound cultures
• Research shows that even when S. aureus is cultured from skin swabs, β-hemolytic streptococci are often the true pathogen 3
• The only documented case of enterococcal cellulitis in the literature involves orbital cellulitis 4, an anatomically distinct and unusual presentation

Treatment Algorithm

For typical cellulitis with S. aureus cultured:

1. Assess the clinical presentation:

   • Nonpurulent cellulitis (no drainage, no abscess): Target streptococci primarily; S. aureus coverage only if systemic toxicity or failure to respond to β-lactam 2
   • Purulent cellulitis (drainage present but no drainable abscess): Cover S. aureus empirically 2

2. Determine if MRSA or MSSA:

   • MSSA: Use cefazolin, nafcillin, or oxacillin 1
   • MRSA: Use vancomycin, daptomycin, linezolid, or clindamycin (if local resistance <10%) 2

3. Duration: 5-10 days for outpatients, 7-14 days for hospitalized patients with complicated SSTI 2

4. Ignore the enterococcus unless:

   • Patient fails appropriate S. aureus therapy
   • There are specific risk factors (immunocompromised, post-surgical wound, diabetic foot infection with deep tissue involvement)
   • Clinical deterioration despite adequate staphylococcal coverage

Common Pitfalls to Avoid

Do not reflexively treat all organisms grown in culture. This leads to unnecessary broad-spectrum antibiotic use, increased resistance, and potential adverse effects. The research demonstrates that polymicrobial cultures often reflect surface contamination rather than true infection 3.

Do not assume wound cultures accurately reflect the causative pathogen in cellulitis. Studies show that β-hemolytic streptococci cause 72-85% of cellulitis cases 3, yet they are rarely cultured because they reside in deeper tissues, not on the wound surface where swabs are obtained.

If you must cover enterococcus (immunocompromised host, necrotizing infection, post-surgical wound), add ampicillin or amoxicillin to your staphylococcal regimen. However, this scenario is uncommon in typical cellulitis.

Clinical Context

The evidence strongly suggests that treating based on clinical presentation rather than wound culture results leads to better outcomes 1, 5. The IDSA guidelines emphasize that typical cellulitis should receive streptococcal coverage, with staphylococcal coverage added only for specific clinical scenarios 1, 2. The rare enterococcal growth in your case almost certainly represents colonization, not infection requiring treatment.