Microbial synergy in experimental intra-abdominal abscess

Intra-abdominal sepsis was studied in Wistar rats by using four microbial species: Escherichia coli, enterococci, Bacteroides fragilis, and Fusobacterium varium. These organisms were implanted into the peritoneal cavity singly and in all possible dual combinations. Results were evaluated by mortality rates and the incidence of intra-abdominal abscesses on autopsy following sacrifice after 7 days. Mortality was restricted to recipients of E. coli, thus implicating coliforms in the acute lethality associated with this experimental model. Intra-abdominal abscesses were produced in 61 of 95 (94%) animals that received the combination of an anaerobe and a facultative organism. Abscesses failed to form with any single strain or with E. coli plus enterococci, and they were detected in one 1 of 19 animals receiving B. fragilis plus F. varium. These results suggest that intra-abdominal abscess formation is related to synergy between anaerobes and facultative bacteria.