Experimental intraabdominal abscess formation by Escherichia coli and bacteroides fragilis.

An improved animal model of intraperitoneal abscess formation was developed in order to study the role of Bacteroides fragilis and Escherichia coli. Both microorganisms were found to independently cause abscesses, although Bacteroides fragilis-induced abscesses were invariably minute. The combined inoculation of these microorganisms resulted in the induction of intraabdominal abscesses larger than those formed by Bacteroides fragilis or Escherichia coli alone. However, the size difference between abscesses produced by Escherichia coli alone and by the combination of both organisms was not statistically significant. The animal model defined in this study differed from earlier models in that use of the complex sterile cecal contents can be avoided. This allows for a more precise evaluation of the contribution of each organism to the pathogenic process of intraabdominal abscess formation.