Murine Wound Infection Model for Pathogenesis

Mouse wound infections were modified from a previous study [39 (link)]. Male C57BL/6 mice (7–8 weeks old, 22 to 25 g; InVivos, Singapore) were anesthetized with 3% isoflurane and the dorsal hair trimmed. Following trimming, Nair cream (Church and Dwight Co) was applied and the fine hair removed via shaving with a scalpel. This 2-step shaving method ensured the wound dressing remains for >5 days without detachment. The skin was then disinfected with 70% ethanol. A 6-mm biopsy punch (Integra Miltex, New York) was used to create a full-thickness wound and 10 μL of the respective bacteria inoculum applied. The wound site was then sealed with a transparent dressing (Tegaderm, 3M, St Paul Minnesota). At indicated time points, mice were euthanized and a 1 × 1 cm piece of skin surrounding the wound site was excised into sterile phosphate buffered saline (PBS). Excised wounds were homogenized and viable bacteria enumerated by plating onto BHI agar with (Supplementary Table 1) and without antibiotics to check for contamination. Mice with contaminants were excluded from our datasets and subsequent analysis. For coinfection experiments, competitive index (CI) was determined with the following formula: $\text{CI}=\left(\text{OG1RF}\left(\text{output}\right)/\text{OG1X}\left(\text{output}\right)\right)/\left(\text{OG1RF}\left(\text{input}\right)/\text{OG1X}\left(\text{input}\right)\right)$