Resistance emergence among P. aenrginosa in a rat thigh-abscess model. Comparison of imipenem and meropenem treatment

Resistance emergence to carbapenem antibiotics was studied in a rat-thigh abscess model. Abscesses were developed in three groups with a total of 15 P. aeruginosa strains (three rats per strain). Groups were assigned to imipenem or meropenem treatment while one was left antibiotic-free. Test strains were fully susceptible to these antibiotics and the "Mutant Preventing Concentrations" of imipenem and meropenem over these strains were comparable. Antibiotic serum levels, assessed by serum bioassay test, were similar among therats. After four days, rats (n=45) were sacrificed and carbapenem resistant mutants were selected on imipenem (4 mg/L) and meropenem (4 mg/L) supplemented agar plates. Resistant variants of three strains, from four abscesses, were detected; one in the meropenem group, two in the imipenem and one in the untreated group. The MICs of imipenem and meropenem for the mutants were increased fourfold times or even higher of their counterparts. Resistance emergence under antibiotic pressure in P. aeruginosa has been shown in various conditions. To our knowledge, however, resistance emergence in abscess and also the comparison of imipenem and meropenem in this regard has not been studied before.