Traumatic liver injury increases susceptibility to bacterial pneumonia in swine

In this study, we develop a standardized porcine model of distant injury plus lung bacterial inoculation to allow translational investigations of the effects of tissue injury on susceptibility to infection. This generalizable model will allow testing of immune interventions on the evolution of infection.

A standardized liver crush (5 cm × 2.5 cm/3 kg) plus hemoperitoneum (6 mL/kg) or sham procedure was performed in 30-kg Yorkshire pigs, followed by intratracheal inoculation of bacteria ( Actinobacillus pleuropneumoniae ). We then compared gross pathology, histology, lung bacterial counts, danger-associated molecular pattern molecules, and serum cytokines between the two groups.

The lungs of injured pigs demonstrated significantly enhanced responses to infection compared with sham injured pigs, both on the macroscopic and microscopic levels. Lung bacterial clearance was significantly impaired after trauma, with increased infiltration of neutrophils and differential location of myeloid cells on immunostaining. In lung parenchyma expression of the stress response genes, Hmox1 and Nrf2 were increased in both trauma alone and trauma plus infection. Plasma from pigs subjected to trauma showed increased levels of the danger-associated molecular patters heme and mitochondrial DNA and promoted bacterial growth in vitro compared with plasma from uninjured pigs.

We have developed a novel, clinically relevant, reproducible porcine model of abdominal injury with subsequent A. pleuropneumoniae pneumonia for the study and development of therapeutics against immune dysregulation induced by trauma. Additionally, a novel finding is that plasma from traumatized pigs provides a permissive environment for bacterial growth.