Understanding the host inflammatory response to wound infection: An in vivo study of Klebsiella pneumoniae in a rabbit ear wound model

Abstract

Wound infection development is critically dependent on the complex interactions between bacteria and host. Klebsiella pneumoniae has become an increasingly common wound pathogen, but its natural history within wounds has never been studied. Using a validated, in vivo rabbit ear model, wounds were inoculated with K. pneumoniae at different concentrations (10²-10⁷ colony-forming units) with measurement of viable and nonviable bacterial counts, histological wound-healing parameters, and host inflammatory gene expression at multiple time points postinoculation (48, 96, and 240 hours). Bacteria and wound morphologies were evaluated with scanning electron microscopy. Comparable experiments were performed in ischemic ears to model immune response impairment. All wounds, despite different inoculants, equilibrated to similar bacterial concentrations by 96 hours. With a 10⁶ colony-forming units inoculant, wounds at 240 hours showed decreased bacterial counts (p < 0.01), with a corresponding improvement in healing (p < 0.01) and a decrease in inflammatory response (p < 0.05). In contrast, ischemic wounds revealed impaired inflammatory gene expression (p < 0.05) resulting in higher steady-state bacterial concentrations (p < 0.01), impaired healing (p < 0.05), and biofilm formation on scanning electron microscopy. We conclude that a normal inflammatory response can effectively stabilize and overcome a K. pneumoniae wound infection. An impaired host cannot control this bacterial burden, preventing adequate healing while allowing bacteria to establish a chronic presence. Our novel study quantitatively validates the host immune response as integral to wound infection dynamics.

Biofilms and Wounds: An Overview of the Evidence

“…The uninfected controls healed quicker than the P. aeruginosa infected wounds, which were confirmed to be in a biofilm by the presence of microcolonies or aggregates of cells, as shown with SEM. Seth et al 25 also used a rabbit ear model to study the effect of Klebsiella pneumoniae on wound healing, confirming biofilm as cellular aggregates by SEM. Later, Seth et al 26 developed dermal punch wounds in white rabbit ears and inoculated them with K. pneumoniae, S. aureus, or P. aeruginosa.…”

Chronic Wound Biofilm Model

“…Outcomes such as impairment of epithelialization, overabundance of granulation tissue, and a hyperinflammatory state are interesting. 8,26,[40][41][42][43] However, reported studies involve short-term infection disallowing prolonged interaction between polymicrobial pathogens and the host. In that respect, the rabbit ear model suffers from limitations comparable to those discussed for the rodent models.…”

“…2 Persistent infection may not only arrest growth of the repairing tissue but it is also known to substantially modify the inflammatory response compromising timely resolution. [3][4][5] The influence of wound infection on the healing process may depend on the following factors: (1) wound etiology, dimension, tissues involved, and anatomical location, 6,7 (2) host factors and response, 8,9 (3) composition of polymicrobial species, 10,11 and (4) state of infection, that is, planktonic and/or biofilm. Biofilm-infected wounds suffer from compromised closure.…”

Pseudomonas aeruginosa quorum-sensing signaling molecule N-3-oxododecanoyl homoserine lactone induces matrix metalloproteinase 9 expression via the AP1 pathway in rat fibroblasts

“…8) Seth et al also demonstrated that impaired host immunity allows bacteria to establish wound infection. 32) In contrast, Kanno et al reported accelerated wound healing following PAO-1 inoculation 33) or 3OC12-HSL administration, 34) thus supporting the latter situation. Future studies are needed to explore this hypothesis.…”