What type of laboratory is recommended for a wound culture?

Laboratory Recommendations for Wound Culture

For wound cultures, tissue biopsy or aspirate specimens from the advancing margin of the wound are strongly recommended over surface swabs, as they provide more accurate representation of the infectious process.

Optimal Specimen Collection Techniques

• The specimen of choice is a biopsied sample of the advancing margin of the lesion, as pus alone or a cursory surface swab is inadequate and does not represent the true disease process 1
• Prior to specimen collection, the wound should be thoroughly cleansed and devoid of topical antimicrobials that can affect culture results 1
• Tissue specimens obtained by biopsy or curettage are more reliable than swabs for determining true pathogens 2
• When collecting specimens, be specific about body site and type of wound (for example "human bite wound, knuckle") rather than using the generic label "wound" 1

Specific Wound Type Considerations

Burn Wound Infections

• Quantitative culture of either surface swab or tissue biopsy is recommended for monitoring burn wound infections 1
• Tissue biopsy is preferred as swab cultures only reflect surface flora rather than the advancing margin of infection 1
• Quantitative bacterial culture of tissue biopsy should be supplemented with histopathological examination to better assess microbial invasion 1

Human and Animal Bite Wounds

• For human bite wounds, tissue or aspirate specimens should be collected for both aerobic and anaerobic cultures 1, 3
• Human bite infections are typically polymicrobial, involving both aerobic and anaerobic bacteria from the oral cavity 3
• For animal bites, cultures should focus on common pathogens like Pasteurella species, streptococci, and staphylococci 1

Trauma-Associated Infections

• Specimens should not be submitted for culture within the first 48 hours post-trauma as growth likely represents environmental contamination 1
• The optimal time to acquire cultures is immediately post-debridement of the trauma site 1

Laboratory Processing Considerations

• Not all laboratories provide quantitative cultures for wound assessment, especially for burn wounds 1
• Consult with the laboratory if specialized services are needed so arrangements can be made for specimen transfer to a reference laboratory 1
• Both aerobic and anaerobic cultures should be obtained, particularly for bite wounds and deep tissue infections 3, 4
• Gram stain should be performed to assess for indicators of inflammation, superficial contamination, and microorganisms 1

Common Pitfalls to Avoid

• Relying solely on swab cultures for diagnosis of wound infection 2, 5
• Failing to properly cleanse and debride the wound before specimen collection 2
• Not considering the wound type and location when interpreting culture results 2
• Requesting the laboratory to "report everything that grows," which can lead to treatment of colonizing organisms rather than true pathogens 1
• Misinterpreting multiple organisms (especially when 8 or more are present) as infection rather than contamination 2

Interpretation of Results

• Cultures from superficial lesions often yield a mixture of pathogens, colonizing organisms, and contaminants 2
• The presence of multiple organisms is more consistent with contamination than true infection, especially if collected by swab 2
• Base treatment decisions on clinical signs of infection rather than solely on culture results showing multiple organisms 2
• For wounds with multiple organisms, focus treatment on the most virulent pathogens rather than treating all cultured organisms 2