Biopsy of lesion or skin - culture

Role

Skin/wound culture identifies bacterial, fungal, or mycobacterial organisms from a skin lesion - distinct from tissue biopsy for histology, and used when infection (rather than inflammatory/neoplastic disease) is the leading differential
Routine in suspected skin/soft tissue infection, particularly when empirical treatment has failed or an atypical organism is suspected

Swab or tissue culture samples are processed on appropriate selective media depending on the suspected organism class (bacterial, fungal, or mycobacterial media each requiring different, sometimes prolonged, incubation conditions) - mycobacterial culture in particular requires specific request and extended incubation (weeks), so must be explicitly requested if atypical mycobacterial infection is suspected, rather than assumed to be covered by standard bacterial culture

Tissue culture (from a biopsy) generally has higher sensitivity than a surface swab, particularly for deeper or less heavily colonised infections, since a swab preferentially samples surface flora/contamination rather than the actual infecting organism at the relevant tissue depth
Correlate culture results with clinical context - a positive culture from a chronically colonised wound (e.g. a venous ulcer) does not necessarily indicate the organism is causing active infection requiring treatment, as opposed to simple surface colonisation

Targeted antimicrobial therapy once the organism and sensitivities are known, rather than continuing empirical broad-spectrum treatment
Atypical/slow-growing organisms (mycobacteria, some fungi) require specific advance discussion with the laboratory to ensure appropriate culture conditions are used

Chronic wound colonisation vs infection, atypical mycobacterial skin infection, fungal skin infection, cellulitis/abscess microbiology

A negative standard bacterial culture does not exclude infection if an atypical organism (mycobacterial, fungal) is genuinely suspected - these require specific, separately requested culture conditions and should be actively considered and requested rather than assumed to be covered by a routine swab

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