Collection of wound exudate: eight samples of wound exudate will be collected in total. The wound site will be dried with cotton pellets and periopaper strips (ProFlow, Amityville, NY, USA) will be gently pressed on the wound for 20 s. In case of blood contamination, the strip is discharged and the sampling is repeated after five min. The volume of exudate is recorded using a Peritron 8000 (Proflow) and expressed in µL. One strip holds approximately 0.1-0.4 µL of exudate. The strips are then transferred to plastic tubes and stored at -80 until further analysis.