Should a wound culture be performed under aerobic, anaerobic, or both conditions?

Wound Cultures Should Be Performed Under Both Aerobic and Anaerobic Conditions

Wound specimens should be sent for both aerobic and anaerobic culture to maximize pathogen recovery and guide appropriate antimicrobial therapy. 1

Rationale for Both Aerobic and Anaerobic Cultures

• Infected wounds frequently contain both aerobic and anaerobic bacteria that contribute to pathogenesis
• Anaerobic organisms are present in up to 17.2% of chronic wound infections 2
• Failure to identify anaerobic pathogens may lead to inappropriate antimicrobial selection and treatment failure
• Guidelines specifically recommend sending specimens "for aerobic and anaerobic culture" 1

Proper Specimen Collection Technique

1. Cleanse and debride the wound before obtaining specimens (essential first step)

2. Obtain tissue specimens from the debrided base using:

   • Curettage (scraping with sterile dermal curette or scalpel blade)
   • Biopsy (bedside or operative)
   • Aspiration of purulent collections

3. Avoid swabbing undebrided ulcers or wound drainage

   • If swabbing is the only option, use a swab designed for both aerobic and anaerobic organisms 1

4. Transport properly:

   • Use appropriate sterile container or transport media
   • For anaerobic specimens: transport at least 0.5 mL of fluid or 0.5 g of tissue in an anaerobic transport tube 3
   • For aerobic bacteria: Consider inoculating 1-10 mL of fluid directly into an aerobic blood culture bottle 3

When to Culture

• Culture all clinically infected wounds except possibly mild infections in antibiotic-naïve patients at low risk for MRSA 1
• Do not culture clinically uninfected lesions unless for epidemiological purposes 1
• Cultures are particularly important for:
  • Patients with systemic symptoms suggesting bacteremia
  • Those who have failed initial therapy
  • Complex or recurrent infections
  • Patients with healthcare exposure or prior antibiotic use 3

Limitations of Culture Methods

• Standard cultures identify only a small percentage of microorganisms present in wounds 1
• Molecular microbiological techniques can detect more organisms and provide results faster 1
• In one study, 338 different bacterial taxa were identified with molecular testing compared to only 17 with culture methods 4

Common Pitfalls to Avoid

1. Don't swab undebrided wounds - this primarily detects surface colonizers rather than true pathogens
2. Don't delay antimicrobial therapy to obtain cultures if the patient appears septic
3. Don't rely on aerobic cultures alone - this will miss potentially important anaerobic pathogens
4. Don't collect specimens after starting antibiotics if possible - this reduces culture yield

By following these guidelines for proper specimen collection and requesting both aerobic and anaerobic cultures, clinicians can maximize the identification of causative pathogens and optimize antimicrobial therapy, ultimately improving patient outcomes.