A new model of bacterial peritonitis in mice for evaluation of antibiotics. Effects of aspoxicillin and piperacillin.

: Experimental peritonitis was produced in mice with Escherichia coli TPRL 10760 derived from the intestinal flora of mouse and used to evaluate the chemotherapeutic effects of semisynthetic penicillins, aspoxicillin (ASPC) and piperacillin (PIPC). The peritonitis was induced by inserting a gelatin capsule containing the bacterial cells, sterilized cecal contents and BaSO4 into the pelvic cavity of an anesthetized mouse. Infection with more than 10(6) colony forming units (CFU) of the bacteria/mouse resulted in an acute peritonitis associated with 100% mortality, whereas an inoculum size of 10(2) CFU/mouse produced a chronic peritonitis. In the mice with acute peritonitis, administration of 100 mg/kg x 5 times of ASPC reduced the mortality to 0% but administration of 100 mg/kg x 5 times of PIPC did not reduce the mortality. In the mice with chronic peritonitis, ASPC was more effective than PIPC in decreasing the number of viable bacterial cells in the peritoneal fluid. The superiority of ASPC over PIPC was attributable to its higher bactericidal activity as well as its high drug level and more persistency in the peritoneal fluid as compared to PIPC.