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Introduction: Infection is a devastating complication of burn wounds, with sepsis accounting for up to 60% of burn related deaths, despite advances in antibiotic treatment. Pseudomonas is the most frequently implicated pathogen, invading systemically after burn wound colonization and often resistant to antibiotics. Local application of probiotics, specifically Lactobacillus plantarum (Lp) in the burn setting is attractive as a novel therapeutic intervention, potentially modulating infection by competitively inhibiting pathogen colonization and regulating immune response. Our previous studies in a rabbit burn model show that application of Lp to burn wounds limits Pseudomonas aeruginosa (Pa) bioburden within the wound, thus showing potential to prevent progression to burn wound sepsis. The implication of this for improvement of burn survival is tremendous. In this study, we hypothesize that local application of probiotics(Lp) to burn wounds will prevent death in a mouse burn wound-sepsis model.
Methods: A non-lethal burn wound model was established using a 1cm diameter brass stamp heated to 80°C and applied for 20 seconds to the paraspinal region of CBL57 mice. A subsequent burn-sepsis model was established by sub-eschar injection of 1x10^7 cfu of bioluminescent Pa 24 hours after burn. The intensity of Pa infection was tracked daily using IVIS imaging of bioluminescence. Animals were monitored closely until death/moribund status, then sacrificed and organs, wound tissue, and blood collected. Finally, the effect of Lp was tested by giving daily sub-eschar injections of 1x10^9 cfu of Lp at post burn day 0-4, along with standard Pa injection on post burn day 1. These animals were monitored until death or one week, when they were sacrificed and tissues harvested. All tissues and organs harvested were subjected immediately to IVIS imaging and PCR to measure bacterial load. Six mice served as control group 1 (burn alone), six mice as control group 2 (burn + daily Lp), 13 mice as experimental group 1 (burn + Pa), and 13mice as experimental group 2 (burn + Pa + daily Lp).
Results: 100% survival was observed in control groups 1 and 2. None of these animals demonstrated Pa colonization in wound, blood, or organs on IVIS imaging. 92% mortality and 100% morbidity within 40hours was observed in experimental group 1. All animals demonstrated positive bioluminescence of wound, liver, and occasionally lung, demonstrating systemic Pa translocation. The one surviving animal sustained permanent hindlimb paralysis. With the intervention of daily Lp in experimental group 2, mortality decreased to 7.6%. Additionally, the intensity of bioluminescece in the burn wound decreased substantially faster compared to experimental group 1 and no bioluminescent Pa translocation to internal organs was observed.
Conclusions: Our findings demonstrate that burned animals treated with Lp before and after Pa challenge demonstated both significantly improved survival (8% to 92.4%) and more rapid clearance of Pseudomonal infection from burn wounds. Lactobacillus plantarum shows enormous potential as a probiotic agent to prevent burn wound infection and subsequent death from burn wound sepsis. Our current efforts are directed at clinical application in the burn ICU setting.