Development of Pseudomonas aeruginosa Biofilms in Partial-Thickness Burn Wounds Using a Sprague-Dawley Rat Model.

We used a modified Walker-Mason scald burn rat model to demonstrate that Pseudomonas aeruginosa, a common opportunistic pathogen in the burn ward and notable biofilm former, establishes biofilms within deep partial-thickness burn wounds in rats. Deep partial-thickness burn wounds, similar to 10% of the TBSA, were created in anesthetized male Sprague-Dawley rats (350-450 g; n = 84). Immediately post-burn, 100 mu l of P. aeruginosa in phosphate-buffered saline at 1 x 10(3), 1 x 10(4), or 1 x 10(5) cells/wound was spread over the burn surface. At 1, 3, 7, and 11 days post-burn, animals were euthanized and blood and tissue were collected for complete blood counts, colony-forming unit (CFU) counts, biofilm gene expression, histology, scanning electron microscopy (SEM), and myeloperoxidase activity in the burn eschar. P. aeruginosa developed robust biofilm wound infections, plateauing at similar to 1 x 10(9) CFU/g burn tissue within 7 days regardless of inoculum size. Expression of Pseudomonas alginate genes and other virulence factors in the infected wound indicated formation of mature P. aeruginosa biofilm within the burn eschar. Compared to un-inoculated wounds, P. aeruginosa infection caused both local and systemic immune responses demonstrated by changes in systemic neutrophil counts, histology, and myeloperoxidase activity within the burn wound. Additionally, SEM showed P. aeruginosa enmeshed within an extracellular matrix on the burn surface as well as penetrating 500-600 mu m deep into the eschar. P. aeruginosa establishes biofilms within deep partial-thickness burn wounds and invades deep into the burned tissue. This new in vivo biofilm infection model is valuable for testing novel anti-biofilm agents to advance burn care.