A rat model of non-lethal bacterial infection.

The purpose of the study was to develop a small animal model of intraperitoneal infection without mortality and with a catabolic response to the infection, viz., to mimic the clinical situation in man. Intraperitoneal infection was induced in female Wistar rats by deposition of a gelatin capsule containing a mixture of Escherichia coli and Bacteroides fragilis and adjuvant substances. Seven groups of animals were infected with different bacterial inocula (0.2-4.3 x 10(6) CFU) to establish reproducible and dose-dependent changes in mortality, body weight in relation to food intake, blood cultures, peripheral blood leukocyte counts, and abscess formation on autopsy. No mortality was observed in animals with an inoculum below 2.2 x 10(6) CFU in spite of positive blood cultures. Initial weight loss was followed by weight gain in all animals except the group infected with the low inoculum (0.2 x 10(6) CFU). This group had no mortality, was in a catabolic state for three days, indicated by weight loss in spite of nearly normal food intake, and the infectious state was supported by intraperitoneal dissemination of small abscesses. The low-grade character of the infection was reflected by changes in peripheral blood lymphocyte and neutrophil granulocyte concentrations. In conclusion, this study presents a small animal model with a reproducible dose response to the bacterial challenge, allowing prolonged studies of metabolic changes following infection.