Microbiological testing
Microbiological culture takes several days to provide results and cannot distinguish between colonisation and pathogenic infection. Therefore antimicrobial therapy should be commenced immediately based on the clinical impression of ulcer infection, with microbiology sensitivity results used to guide any subsequent antibiotic switch. Antibiotic therapy should not be delayed until after culture results are available.
If a cultured micro-organism is not sensitive to the initial antibiotics but the wound is healing and clinical signs of infection are decreasing then a change of antibiotics is not be recommended. In this case the wound may have been colonised with one organism while the pathogenic infection was caused by another bacterium.
Microbiological sampling has caused much debate with the standard charcoal swab often the first choice in clinical practice. While the results of some studies suggest rolling a swab over the wound give similar results to those of deep tissue biopsies, most studies have found swabs to be less sensitive and specific. (2) Before any sample is taken careful clinical debridement should have been undertaken and if any deep tissue or bone was extracted then this itself can be sent for culture. Below is a list of sampling techniques that can be used:
- Wound swab
- Needle aspiration
- Irrigation
- Curettage of ulcer base
- Punch biopsy
- Deep tissue specimens
- Bone biopsy
The best results are normally obtained from tissue or pus samples, preferably taken at a level deeper than superficial tissue.
