The development of an infected acute wound porcine model
D. Boone, MD, E. Braitman, MD, J. Afthinos, MD, C. Gendics, RN, E. Sordillo, MD, PhD, G. Todd, MD, J. Lantis, MD
Introduction: To assess the many potential antimicrobial agents available as well as pro-growth agents, we found it necessary to develop a medium size animal model. While there are many animal models for infection, many of them include a wound inhibiting therapy, as an adjunct. In addition, in most models there is not a delay between inoculation and treatment. Therefore, making the models suboptimal to assess the treatment on critical colonization.
Methods: A total of 12 animals (50-kg pigs) had four 6-cm in diameter full-thickness wounds created. The reservoir of the wound was filled with a mixture of Pseudomonas aeruginosa, Staphylococcus aureus, and Bacteroides fragilis in a ratio of 2:2:1 at a concentration of 10⁷ CFU/cc. A standard gauze was then placed in the wound and covered with a bio-occlusive dressing. Quantitative biopsies and semi-quantitative swabs were obtained at 72 hours, in addition histologic biopsies and digital images were obtained at this point in time. At that point therapeutic device assays were initiated.
Results: One animal suffered a postoperative fatality of unknown etiology. One animal was euthanized secondary to an unrecognized medical comorbidity. Of the 40 remaining wounds, all were clinically infected. Two of the animals (8 wounds) required systemic antibiotic prior to their first biopsy due the wounds exhibiting local infection signs, and the animals exhibiting fever and tachycardia. All wounds showed significant bacterial counts and histological markers of infection. The 2 animals (8 wounds) that received antibiotics had significantly lower bacterial wound counts.
Conclusions: We were able to create an effective model for invasive bacteria infection without systematically impairing the host. However, the classic teaching that systemic antibiotics do not effect the local wound bacterial burden may not be true, based upon the local wound environment findings from the 2 animals treated with systemic antibiotics.

Bacterial burden and wound outcomes as influenced by negative pressure wound therapy
D. Boone, MD, E. Braitman, MD, J. Afthinos, MD, C. Gendics, RN, E. Sordillo, MD, PhD, G. Todd, MD, J. Lantis, MD
Introduction: While we continue to be aware that Negative Pressure Wound Therapy (NPWT) provides significant clinical benefits, we remain somewhat ignorant as to the mechanism through which it works. Some investigators have postulated that mechanical removal of bacteria may play a role. To facilitate this process, a theoretically bacteriocidal (Silver) sponge has been added to the NPWT technology. In order to understand the effect of NPWT on bacterial burden and wound response we treated a porcine infected wound model with NPWT and NPWT with silver dressing.
Methods: Sixteen chronically infected (Pseudomonas, S aureus, Bacteroides fragilis) wounds in a porcine model (described in separate submission) were treated with NPWT standard foam or silver foam for a period of 7 days with 3 dressing changes. At each dressing change quantitative, semi-quantitative bacterial cultures, histological samples, and digital photographs were taken.
Results: The wounds continued to show gross and microscopic improvement when treated with NPWT and NPWT with silver in comparison moist wound care controls. However, the bacterial burden continued to increase and broaden to include local skin flora that had been absent immediately after wounding. These increases in bacteria were not affected by the use of silver dressings.