Wound swabs are done commonly to look for the causative bacteria 

• Explain the procedure to the patient and the attendees
• Make sure that no antibacterial cream is applied. 
• If the wound is dry and crusty, you can put a few drops of sterile water and proceed as below.
• Wash hands with antibacterial soap and water or use the bactericidal hand solution. Wear gloves.
• Using the swab rub it on the surface of the wound or the place of exudate
• If you can get bits of crusty discharge, you can collect it as well.
• Place the specimens in an appropriate container with the details of the patients and the type of specimen and send it to the lab
• Make sure you document it