DermatologyTier 2Topic

Wound swab - bacterial

Role

Bacterial wound swab culture identifies the causative organism(s) and antibiotic susceptibility in a clinically infected wound - guiding targeted antibiotic therapy and distinguishing true infection from colonisation
Wound infection is common across surgical, traumatic, and chronic (e.g. venous/diabetic) wounds, with polymicrobial colonisation the norm in chronic wounds specifically - making clinical correlation essential to interpretation

Colonisation vs infection

All chronic wounds are colonised with bacteria - a positive swab culture in the absence of clinical infection signs (increasing pain, spreading erythema, purulent discharge, systemic symptoms) reflects colonisation, not infection requiring treatment
True infection involves bacterial invasion of viable tissue provoking a host inflammatory response, distinguishing it from surface colonisation which does not require antibiotic treatment

Technique and interpretation

Swab technique matters: a deep swab of the wound bed after debridement/cleaning (not surface exudate or slough) improves yield and reduces contamination with colonising surface flora
Clinical correlation is essential - culture results should be interpreted alongside clinical signs of infection (spreading erythema, increasing pain, purulent discharge, systemic symptoms), not treated in isolation

Acting on the result

Clinically infected wound -> targeted antibiotics guided by culture and sensitivity, alongside appropriate wound care (debridement, dressing selection)
Colonised but clinically uninfected wound -> no antibiotic treatment indicated - treating colonisation drives antimicrobial resistance without benefiting the patient, and appropriate wound care (not antibiotics) remains the correct management

Settings

Chronic venous/diabetic foot ulcers (commonly colonised), surgical site infection, cellulitis (a clinical diagnosis that does not require a wound swab if there is no open wound/discharge), antimicrobial stewardship (avoiding antibiotic treatment of colonisation)

Key point

The distinction between colonisation and true infection is the central, frequently tested principle - a positive culture from a chronic wound without clinical infection signs should not trigger antibiotic treatment, which is a core antimicrobial stewardship point relevant across chronic wound management

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