Microbiology of postoperative peritonitis

Abstract Background The microbiology of secondary peritonitis is well known and standards of antibiotic therapy are established. In contrast, little is known about the bacteriology of postoperative peritonitis. Resistant strains could be involved and patients may have had previous antibiotic treatment. Methods The intraoperative and postoperative bacteriology (10 days after operation) of all 88 cases of postoperative peritonitis occurring between September 1994 and May 1999 were documented. Resistances were used to determine effective antibiotic therapy. Results Compared with secondary peritonitis, enterococci outnumbered Escherichia coli in postoperative peritonitis. While E. coli showed no advanced resistance, the different pattern of bacterial findings (e.g. enterococci, Enterobacter, Gram-positive bacteria) leads to failures of standard therapy for secondary peritonitis. Imipenem–cilastatin failed in 20 per cent, piperacillin–tazobactam in 31, aminoglycosides in 31, ciprofloxacin in 37 and third-generation cephalosporins in 47 per cent (the latter three combined with metronidazole). Conclusion Cephalosporins, the ‘gold standard’ in secondary peritonitis, fail in postoperative cases. Carbapenems are the drugs of choice. Aminoglycosides should be avoided in these patients.