Manipulation of the size and clone of an intra-abdominal abscess in rats

A rat grading model of chronic sepsis was developed by inoculation of a small (0.8 ml) or a large (1.5 ml) fecal pellet consisting of sterile rat feces, agar and a known number and strain of bacteria. A uniform spherical abscess containing Escherichia coli and Bacteroides fragilis was formed in 100% of the animals that survived the initial peritonitis stage. The effects of a large biclonal abscess were compared with those of a small abscess and of a sham operation. The peritonitis stage with high mortality was followed by an abscess stage. In rats with a large abscess, net body weight did not increase and there was 16% mortality during the abscess stage. On the 7th day, severe hepatic energy deficiency and lactic acidosis occurred in the septic liver with B. fragilis bacteremia. Rats with small abscesses showed mild metabolic disturbances with no mortality. Standardization of rat models with chronic graded septic abscess is possible by controlling the size of the fecal pellet and the species and number of inoculated bacteria.