Development of an experimental model of infected skin ulcer

Abstract

A model of infected skin ulceration could prove useful in assessing the clinical effectiveness of antimicrobial ointments and dressings. However, no such models have been previously established. Three types of wound were induced in rats: full-thickness wounds covered with gauze, burn wounds and wounds resulting from mechanical trauma. Wounds were inoculated with S. aureus or P. aeruginosa. Persistent infected wounds were observed only in full-thickness wounds covered with gauze. In a second experiment, colonies of P. aeruginosa or S. aureus were counted within 15 x 15 mm full-thickness wounds covered with gauze. Wounds were inoculated with 1.0 x 10(6) colony-forming units (CFU) of P. aeruginosa or S. aureus and then sealed to ensure an enclosed environment. Tissue bacterial counts exceeded 10(6) CFU/g from the next day until day 9 after infection. Bacterial counts exceeded 10(8) CFU/ml in wound exudate collected between days 1 and 7. We have developed a model of wound infection in which persistence of infection can be achieved for 9 days following ulceration due to the application of gauze to the base of a full-thickness wound.

Figure 1

Macroscopic appearances of the wound without gauze 7 days after inoculation with S. aureus. Marked wound contraction was observed with minimal exudate.

Figure 2

Macroscopic appearances of the wound with gauze 7 days after inoculation with S. aureus. Purulent wound exudation was observed.

Figure 3

Bacterial counts in tissue biopsies from infected wounds inoculated with S. aureus (–▪–) or P. aeruginosa (–•–). The points represent mean values for four wounds, and vertical bar represents the standard error of the mean (SEM).

Figure 4

Bacterial counts in wound exudates from infected wounds inoculated with S. aureus (–▪–) or P. aeruginosa (–•–). The points represent mean values for four wounds, and vertical bar represents the standard error of the mean (SEM).