[Antimicrobial activity of carbapenems and the combined effect with aminoglycoside against recent clinical isolates of Pseudomonas aeruginosa].

The carbapenem susceptibility of 32 strains of Pseudomonas aeruginosa recently isolated in Kakogawa municipal hospital was investigated. The MIC ranges of imipenem, panipenem, and meropenem were 0.25-16 mg/L, 0.5-16 mg/L, and < 0.03-4 mg/L, respectively, and meropenem showed the highest antipseudomonal activity among the three carbapenems tested. In the analysis based on the MIC interpretive standards established by NCCLS, the resistance rates of test strains for imipenem, panipenem, and meropenem were 6.3%, 15.6%, and 0%, respectively. We also investigated the in vitro combined effect of imipenem or meropenem with amikacin against another 20 isolates of P. aeruginosa by checkerboard titration assay. Antagonism (minimum FIC index > 2) was not observed in any combinations against all strains tested. Super-additive effects (minimum FIC index < 1) in the combination of imipenem and amikacin were observed in eight (40%) strains tested. In contrast, in the combination of meropenem and amikacin, super-additive effects were observed in 14 isolates (70%). These results suggested that meropenem is superior to imipenem in combined effect with amikacin against P. aeruginosa. In conclusion, meropenem showed higher antipseudomonal activities than other carbapenems tested in both conditions, alone and in combination with amikacin. With regard to the clinical efficacy and prevention of antibiotic resistance, meropenem monotherapy or combination therapy with aminoglycoside is the most superior treatment for pseudomonal infections, and the findings in this study suggest that meropenem is still clinically very useful.