Background: Pseudomonas aeruginosa (PA) is a leading cause of morbidity and mortality in patients with infected burns. Immunotherapy and vaccination (active or passive) against PA are desirable options in an era of increasing drug resistance. PA flagellum is an important virulence factor, and therefore targeted for immune therapy. We evaluated the efficacy of treatment of PA infection with monoclonal antibodies raised against PA flagellin type-a (anti-aFla), using a murine-infected burn model.
Methods: Groups of 12 mice (CBL57, 18-20 gram) were studied. A full thickness scald burn involving 6-8% of the total body surface area was induced. Infection was induced by an immediate post-burn sub-eschar injection of PA (100 microliter). Study groups included: 1. Immune therapy: 1a. Monoclonal anti-aFla, 1b. Non-specific monoclonal antibodies (NS Ab); 2. Conventional antibiotic: Imipenem (IMP); 3. Model control: Untreated infected-burn. Anti-aFla was given intra-peritoneal once daily for 4 days (50 microgram x 4), and NS Ab treatment was given similarly. IMP treatment was given intra-peritoneal twice daily for 4 days (0.5mg x 2). Mortality and morbidity (weight change and functional score) follow-up was 2 weeks. Bacterial counts from the burn and spleen were performed 6, 24 and 48 hours after infection was induced. Burn histopathology was examined on days 2 and 14 after infection induction.
Results: In our murine infected burn wound model, mice infected with PA (3x105 CFU), mortality rate was 92%. Treatment with anti-aFla reduced the mortality rate to none (P<0.0001), which was similar to the IMP treated group. The mortality rate in the NS Ab treated group was 100%. Morbidity, as expressed by weight loss and functional activity score, paralleled survival results. In groups treated with anti-aFla or IMP, the weight loss was of lesser magnitude than in the untreated and NS Ab treated groups (P<0.05). Bacterial load in the spleen was significantly lower in mice treated with anti aFla compared to the non-treated group (P=0.01). Burn histology in the untreated infected burn group demonstrated full-thickness necrosis with intramuscular abscesses, as opposed to mild inflammation and fibrosis in the dermis and regenerative epidermal changes in the anti-aFla treated group. Conclusion: Anti-aFla Ab is effective in reducing mortality and morbidity in murine PA infected burn model. In this era of increasing antibiotic resistance, specific immune therapy is a promising modality for prevention and treatment of infected burns.