Despite optimal treatment some wounds are slow to heal. The challenge clinically and microbiologically is to identify those wounds in which healing is impaired as a result of infection or heavy bacterial burden and in which systemic or topical antimicrobial treatment will be of benefit.

A charcoal swab preserves bacteria during transport to the laboratory

Staphylococci and streptococci are the most commonly encountered pathogenic organisms in community acquired superficial wounds. More unusual organisms may be found in bite wounds, and these reflect the source of the bite. Pathogenic organisms causing surgical wound infections vary according to the anatomical site of surgery. Antibiotic resistant organisms, such as methicillin resistant Staphylococcus aureus (MRSA), are more commonly encountered, reflecting the hospital flora.

Punch biopsy for microbiological analysis

When to sample

It is inappropriate to swab all wounds: swabs should be taken only from overtly infected wounds and from wounds that are deteriorating, increasing in size, or failing to make satisfactory progress despite an optimal environment for wound healing. Indicators of wound infection include redness, swelling, purulent exudate, smell, pain, and systemic illness in the absence of other foci. Subtle signs of local wound infection include unhealthy “foamy” granulation tissue, contact bleeding, tissue breakdown, and epithelial bridging. Staphylococcus aureus

Semiquantitative analysis of swab showing light or scanty, moderate, and heavy growth of Staphylococcus aureus