Comparative Analysis of Three Methods for Determination of Imipenem Resistance in Pseudomonas aeruginosa

Background: These days, the antibiotic resistance of Pseudomonas aeruginosa isolates to imipenem has significantly increased. Therefore the study of resistance to imipenem in this organism to imipenem in determining the appropriate treatment is crucial and necessary. The goal of this study is to compare three phenotypic methods of E-test, disk diffusion and micro broth dilution in the study of resistance to imipenem in clinical isolates of P. aeruginosa. Methods: Within a 6-month interval, 120 clinical specimens were collected and evaluated. All isolates were identified as P. aeruginosa by standard biochemical tests and amplification of 16S rRNA gene. Three phenotypic methods of E-test, disk diffusion, and micro broth dilution were used to determine imipenem resistance in P. aeruginosa isolates. Results: Of the 96 P. aeruginosa isolates studied for their resistance to imipenem by the use of E-test, disk diffusion and micro broth dilution methods, 38.5% of the strains in micro broth dilution method and 33.3% in the two methods of E-test and disk diffusion were resistant to imipenem. The rate of sensitivity and specificity of disk diffusion and E-test methods were 100%, 90.1%, and they were 100% and 83.1% for micro broth dilution, respectively. Conclusion: With regard to the results obtained from the comparison of the three methods 100% agreement were observed among the antimicrobial susceptibility results obtained by the E-test and disk diffusion methods (P ≥ 0.05). Therefore, the use of disk diffusion method can be an appropriate replacement for E-test method with regard to its being easy and cost-effective.