Introduction: Despite aggressive interventions, mortality rates for secondary peritonitis, which often occurs as a complication of abdominal surgery, remain high. The aim of this study was to develop a novel animal model of intra-abdominal infection that would determine whether micro-environmental factors present in the intestine of a surgically stressed host play a role in the observed high mortality rates.

Methods: In order to expose a human hospital pathogen to the local microenvironment of the intestinal tract in the presence of surgical injury, 7 week male C57BL6 mice were anesthetized and randomly assigned to undergo either sham laparotomy (Sham) or 30% hepatectomy (Hep) with simultaneous inoculation of 107 CFU of Pseudomonas aeruginosa directly into the cecum. 24 hours later all animals were euthanized and their cecal contents collected for subsequent intraperitoneal injection into a separate group of mice. To accomplish this, 0.03 g cecal contents collected from either sham operated mice (Sham) or hepatectomy mice (Hep) were then implanted into the right lower quadrant of naïve 7 week male C57BL6 mice subjected to either sham laparotomy (Sham) or 30% hepatectomy (Hep).

Animals were followed for mortality and sacrificed once moribund. Cecal contents were also plated for culture to determine the concentration of bacteria in the stool.

Results: Sham operated mice intraperitoneally inoculated with cecal contents from sham operated animals whom had previously been intestinally inoculated with P. aerugionsa (Sham?Sham) were all alive (100% survival) at 24 hours. Mice undergoing hepatectomy (Hep) and intraperitoneal inoculation with cecal contents from sham operated animals previously exposed to intestinal P. aeruginosa (Sham?Hep) had a slightly lower survival rate (66%) (P=NS). However when mice were intraperitoneally inoculated with cecal contents collected from mice undergoing hepatectomy and prior intestinal exposure to P. aeruginosa (i.e. Hep?Sham or Hep?Hep), all mice died of sepsis (100% mortality) (n=6, p<0.05). Stool culture from the two groups demonstrated P. aeruginosa incubated in the mouse gut exposed to hepatectomy (Hep), displayed denser growth and expressed a more virulent phenotype, as judged by the production of pyocyanin.

Conclusion: This study presents a new approach to investigate intra-abdominal sepsis by exposing hospital pathogens to the intestinal environment in the presence of surgical injury with subsequent re-introduction of these organisms to the peritoneum of naïve mice. A more complete understanding of the local microenvironmental cues that shape the virulence of pathogens associated with secondary peritonitis can now be advanced.