2.1. S. aureus-Based Murine Wound Infection Model

Animal experiments were performed with approval of the local State Review Boards of Saarland, Germany (project identification codes 41/2017, approved 19 January 2018, and 30/2018, approved 2 August 2018) and were conducted following the national and European guidelines for the ethical and human treatment of animals. Wounds were introduced in the flanks of female 8- to 12-week-old wild-type (WT), IL-17C-deficient (Il-17c^−/− [12]), and IL-17RE-deficient (Il-17re^−/− [13]) mice (all C57BL/6 background) as described before [14]. In brief, anesthetized mice were treated with carprofen (5 mg/kg bodyweight; Zoetis, Berlin, Germany) and both flanks were shaved and depilated with asid-med hair removal cream (Asid Bonz, Herrenberg, Germany). Skin was disinfected and one full-thickness wound was created on each side with a sterile 5 mm biopsy punch (pfm medical, Köln, Germany). Wounds were stabilized with silicon O-rings (external diameter of 5.5 mm; HUG, Ergolding, Germany) until day 2 to prevent wound healing by contraction and were inoculated with 1 × 10⁵ colony-forming units (CFU) of S. aureus strain Newman [15] or phosphate-buffered saline (PBS) without bacteria (control) directly after wounding. The bacterial inoculum was prepared by diluting bacteria from overnight cultures in tryptic soy broth (TSB; BD, Heidelberg, Germany) to an optical density at 600 nm (OD₆₀₀) of 0.05, and incubating the cultures at 37 °C and 225 rpm with a flask-to-medium ratio of 10:1. After 2–2.5 h of growth, cells were harvested by centrifugation, washed twice with PBS, and resuspended in PBS to an OD₆₀₀ of 0.1 (∼1 × 10⁷ CFU/mL). A 10 µl aliquot of the bacterial solution was spotted onto the wound and allowed to infiltrate into the wound bed for 5 min. Afterwards, wounds were covered with air-permeable Tegaderm films (3M, Neuss, Germany), and animals were monitored daily. At day 6 post-infection, wounds were documented, the mice sacrificed, and the wound areas excised and homogenized in PBS with a hand dispenser (Polytron PT 1200 E Kinematica, Eschbach, Germany). Numbers of CFU were determined by plating serial dilutions on sheep blood agar.