Experimental intra abdominal abscesses in rats. Quantitative bacteriology of infected animals

An animal model stimulating intraabdominal sepsis was produced by implanting large bowel contents into the pelvic region of rats. Bacteriological analysis of infected sites showed quantitative differences according to the stage of disease. During the initial often lethal, peritonitis stage, Escherichia coli (mean concentration, 10⁶/ml), enterococci (10⁵ml) and Bacterioides fragilis (10⁶ml) were always present. Blood cultures obtained during this phase were uniformly positive, with E. coli being the principal isolate. Animals that survived this early acute peritonitis stage developed indolent intraabdominal abscesses. The major isolates in abscess contents were B. fragilis (10 exp. 8.7/ml) were also present but in lesser concentrations. Rank order analysis of these 4 species in peritoneal exudates and abscess pus showed that the 2 aerobes outranked the 2 anaerobes during the early stage of the disease, whereas the reverse was true in abscesses. These experiments also illustrated that a major simplification of the original fecal inoculum occurred, even though the subsequent infection remained bacteriologically complex.