[Resistance to antibiotic treatment produced in a model of experimental Pseudomonas aeruginosa peritonitis]

A mouse model of experimental Pseudomonas aeruginosa peritonitis was used to evaluate the emergence of resistant mutants during antimicrobial therapy. Mice were infected intraperitoneally with a large inoculum (10(8) CFU + 125 mg talcum) of one of eight strains of Pseudomonas aeruginosa and treated for eight hours with imipenem (IPM) (2 mg/kg/60 min), ciprofloxacin (CIP) (5 mg/kg/45 min), ceftazidime (CAZ) (2 mg/kg/45 min), and amikacin (AN) (2 mg/kg/45 min), alone or in combination. Dosages were selected to achieve and maintain for 8 hours intraperitoneal concentrations similar to those seen in human bronchial secretions. Emergence of resistant strains occurred in 88% of mice after IPM, 29% after CIP, and 31% after CAZ. MICs for resistant strains were increased 8-fold to 512-fold above baseline. Given in combination, IPM and CIP use was followed with lower rates of resistance to each drug (6% and 2% respectively) than use of each antimicrobial alone (p less than 0.001). Combination with amikacin reduced resistance rates for all the antimicrobials studied. No resistant strains occurred with the CIP-CAZ combination. Under the experimental conditions used, the CIP-CAZ combination provided the best results, although the difference with the CIP-IPM combination was not statistically significant.