Objective: Our goal was to develop a chronic
wound model in mice that avoids implantation of foreign material or impaired immunity and to use this to characterize the local and systemic immune response associated with
Pseudomonas aeruginosa infection. Approach: We generated bilateral full-thickness dermal
wounds in healthy 10-12-week-old C57Bl6 mice. We waited 24 h to inoculate the developing
wound eschar at these sites. We performed careful titration experiments with luminescent strains of P. aeruginosa to identify bacterial inoculation concentrations that consistently established stable
infections in these animals. We performed flow cytometry-based immunophenotyping of immune cell infiltrates at the
wound site, spleen, and draining lymph nodes over time. Finally, we compared inflammatory responses seen in
wound inoculation with planktonic bacteria, preformed biofilm, and heat-killed (HK) P. aeruginosa. Results: Using this delayed inoculation model and 7.5 ± 2.5 × 102 CFU/mL of PAO1 we consistently established stable
infections that lasted
at 10 days in duration. During early
infection, we detected a strong upregulation of inflammatory
cytokines and neutrophil infiltration at the
wound site, while natural killer (NK) cells and dendritic cells (DCs) were reduced. At the systemic level, only plasmacytoid DCs were increased early in
infection. During later stages, there was systemic upregulation of B cells, T cells, and macrophages, whereas NK cells and
interferon killer DCs were reduced.
Infections with P. aeruginosa biofilms were not more virulent than
infections with planktonic P. aeruginosa, whereas treatment with HK P. aeruginosa only induces a short-term inflammatory state. Innovation: We describe a versatile
wound model of chronic P. aeruginosa
infection that lasts 10 days without causing
sepsis or other excessive morbidity. Conclusion: This model may facilitate the study of chronic
wound infections in immunocompetent mice. Our findings also highlight the induction of early innate immune cell populations during P. aeruginosa
infection.