Elimination patterns of Escherichia coli and bacteroides fragilis from the peritoneal cavity. Studies with experimental peritonitis in pigs.

An animal model for study of bacterial elimination from the peritoneal cavity is presented. Using Escherichia coli and Bacteroides fragilis as infecting agents, two elimination patterns emerged. The patterns were related to the surface properties of the micro-organisms. The concentration of both species was greatly reduced within 2 to 4 hours after peritoneal contamination with 10(10) CFU. The elimination of B. fragilis was contemporaneous with mobilization of granulocytes into the peritoneal cavity, and was probably attributable to bactericidal action of the granulocytes. Most of the E. coli inoculum, however, was cleared before the granulocyte mobilization. Cell-free peritoneal fluid was found to have a bactericidal effect against a rough strain of E. coli, but not against a smooth strain, as demonstrated in vitro. This effect was inhibited by pretreatment of the peritoneal fluid with EDTA, EGTA or heat, which suggested that the alternate pathway of the complement system was involved. In vivo the rough strain of E. coli was rapidly eliminated, while elimination of the smooth strain followed the B. fragilis pattern. It is concluded that bacterial surface properties are important in bacterial peritonitis.