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; St. Luke’s-Roosevelt Hospital Center, New York, NY

Introduction: To assess potential antimicrobial and pro-growth agents available for wound healing, we found it necessary to develop a medium size animal model for infected wounds. While there are many animal models for infection, most of them include a wound inhibiting therapy as an adjunct, which can alter the potential effects of tested therapies. In addition, most models leave no delay between inoculation and treatment, which makes them sub-optimal for assessing treatment of 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, coagulase negative Staphylococcus, and Bacteroides fragilis in a ratio of 2:2:1 at a concentration of 10⁷ cfu/mL. Standard gauze was then placed in the wound and covered with a bio-occlusive dressing. Quantitative biopsy cultures and semi-quantitative swab cultures were obtained at 72 hours; histological biopsies and digital images were also obtained at this point in time. At that point, therapeutic device trials were initiated.

Results: One animal suffered a post-operative fatality of unknown etiology. One animal was euthanized secondary to an unrecognized medical comorbidity. Of the 40 remaining wounds, all became clinically infected, with significant bacterial counts and histological markers of infection. Two of the animals (8 wounds) required systemic antibiotics prior to their first biopsy due to evidence of systemic infection, including fever and tachycardia in addition to grossly infected wounds; the wounds on these two animals were the only ones that failed to achieve the critical bacterial count of 10⁵ cfu/g of tissue.

Conclusions: We were able to create an effective model for invasive bacterial infection without systematically impairing the host. However, the classic teaching that systemic antibiotics do not significantly affect the local wound bacterial burden may not be true, based upon the findings from the two animals treated with systemic antibiotics.

Diagnosing chronic wound infection: comparison of routine cultures, quantitative microbiology, and real time PCR

Yelena Frankel, MD, MPH; Johan Melendez, MS; Lance Price, PhD; Jonathan Zenilman, MD; Gerald Lazarus, MD; Johns Hopkins University, Baltimore, MD

Background: Wounds account for > $15 billion in medical costs in the US. Diagnosing wound infection versus colonization in chronic wounds remains a major clinical challenge. Microbiology labs frequently report qualitative results (scant/moderate/heavy growth) without linkage to clinical outcome and often use a threshold of 10⁵ organisms/g. Reliable quantification of bacterial loads and pathogen speciation are critical to correlating changes in microbial population with healing rates.

Objectives: We evaluated biopsies from chronic wounds and compared quantitative and qualitative results. We determined microbiology by semiquantitative cultures in a clinical lab and quantitative cultures in a research lab. Species detection was compared between quantitative microbiology and real time polymerase chain reaction (RT-PCR).

Methods: 17 patients presenting to an outpatient teaching hospital wound center with suspected chronic wound infection were enrolled. Tissue was obtained from the leading wound edge using a 3-mm curette.