Effect of different combinations of antibiotics on experimental septic peritonitis in rabbits

This study was undertaken to evaluate the efficacy of different combinations of antimicrobial agents in the treatment of experimental septic peritonitis. Two hundred rabbits, divided into ten groups of 20 rabbits each, were used. Septic peritonitis was provoked in two stages: treatment of animals by mechanical lavage or antibiotics was performed during the first stage; blood cultures, isolation and identification of aerobic and anaerobic bacteria in the peritoneal cavity were performed during the second stage. The parameters assessed were survival and, in the second phase, the formation of peritoneal abscesses. The most significant finding was noted in the first phase, where diffuse peritonitis took place, with a very high mortality rate due to bacteremia and sepsis. In both blood and pus from the peritoneal cavity cultures in all groups, Escherichia coli, Klebsiella pneumoniae and Proteus mirabilis (among the aerobes) and Bacteroides fragilis, Clostridium sp. and Peptostreptococcus sp. (among anaerobes) were the predominant pathogens identified. High mortality rates appeared to be due to the aerobic microbes, particularly Escherichia coli, whereas abscess formation was related to the anaerobes, particularly Bacteroides fragilis. All antibiotics tested were effective, whether alone or in combination. Metronidazole, however, was the most effective in the reduction of intraabdominal abscesses. The lowest mortality rate was observed in animals injected with piperacillin and a combination of cefoxitin and an aminoglycoside with metronidazole. Finally, good peritoneal lavage seemed to be as effective as any combination of antibiotic treatment.