Evidence of the proinflammatory role of Enterococcus faecalis in polymicrobial peritonitis in rats

Although the role of members of the Enterobacteriaceae and anaerobes in the pathogenesis of intra-abdominal infections has been extensively demonstrated, the role played by enterococci in these infections remains controversial. The pathophysiological mechanisms induced by enterococci in intra-abdominal infection were studied in a nonfatal model of peritonitis in rats by implanting a gelatin capsule containing Escherichia coli and Bacteroides fragilis with or without increasing concentrations of Enterococcus faecalis or heat-inactivated enterococci. The ability of the rat peritoneal cavity to sterilize itself after bacterial challenge was evaluated by quantifying the inflammatory response in the peritoneal cavity, reflected by both phagocyte and cytokine responses. Effects were evaluated 6, 12, and 24 h and 3 and 6 days after inoculation. On day 6 after inoculation, the highest enterococcal concentration (10(8) CFU/ml) was accompanied by significantly increased concentrations of E. coli in peritoneal fluid and peritoneal phagocytes when compared to other groups. In the first 12 h after inoculation, tumor necrosis factor and interleukin-6 concentrations were significantly increased in the peritoneal fluid of the animals that had received the highest inoculum of enterococci or heat-inactivated enterococci. In the late period of the study (3 and 6 days), significantly increased leukocyte counts were observed in the peritoneal fluid of these animals. These results suggest that E. faecalis somehow inhibited phagocytosis and intracellular killing of the other pathogens and also played an inflammatory role, which might account for the bacterial synergy observed in this model.