Evaluation of carbapenem inactivation method for accurate detection of pseudomonas aeroginosa isolates producing carbapenemase enzymes

Different phenotypic methods are available for identification of pseudomonas aeroginosa isolates producing carbapenemase enzymes. Carbapenem inactivation method (CIM) is a fast and inexpensive way for detection of this enzyme. The purpose of this study was to evaluate the CIM method for accurate identification of carbapenemase producing pseudomonas aeruginosa isolates.

A total of 97 clinical specimens were collected from the patients in the hospitals of Hamadan from November 2017 to May 2018, in Iran. Antibiotic susceptibility test was performed by disc diffusion method. Minimum inhibitory concentration (MIC) for imipenem was measured by E-test. Then, CIM test and polymerase chain reaction (PCR) methods were performed. Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of the CIM test were calculated for each of the genes. Using SPSS16 software, significance of CIM test was evaluated by chi-square test (X2).

In this study, the highest and lowest levels of resistance belonged to cefoxitin 91 (93.8%) and piperacilin/tazobactam 38 )39.2%). Among 97 P. aeruginosa clinical isolates, 49 (50.51%) were carbapenemase producer with positive results for CIM test in 44 (89.7%) isolates, and negative results for CIM test in 48 (49.48%) isolates. Therefore, the sensitivity and specificity of the CIM test were 90% and 100%, respectively.

According to the results of this study CIM method is an inexpensive test which can be easily performed and has high sensitivity and specificity for identification of carbapenemase producing P. aeruginosa isolates.