Early bacterial and inflammatory responses to antibiotic therapy in a model of polymicrobial peritonitis in rats

Abstract

OBJECTIVE: To assess the consequences of different more or less selective treatments on the microbiological and inflammatory responses within the peritoneum. METHODS: The early effects of various antibiotic regimens were evaluated in a model of polymicrobial peritonitis with specifically prepared organisms. Six regimens (amoxycillin plus gentamicin, pefloxacin, ornidazole, pefloxacin plus ornidazole, imipenem and imipenem plus gentamicin) were evaluated at 24 h and 3 days in a non-fatal model of peritonitis in rats achieved by implantation of a capsule containing Escherichia coli, Bacteroides fragilis and Enterococcus faecalis. RESULTS: Therapies that disregarded several organisms were associated with persistence of the strains and an increased peritoneal inflammatory response within the peritoneum. In contrast, therapies active against Enterobacteriaceae and anaerobes were associated with decreases of all the inoculated organisms and a smaller inflammatory response. CONCLUSION: Therapies that disregarded the microorganisms implicated in peritoneal infection are associated with delayed bacterial eradication. The persistence of these organisms within the peritoneal fluid might be involved in prolonged peritoneal inflammation. Although it disregards enterococci, the standard therapy, represented by therapy against Enterobacteriaceae and anaerobes, demonstrates satisfactory effects towards all the inoculated organisms. This apparent contradiction could be related to mechanisms of bacterial synergy.