Evaluation of different conventional phenotypic methods for detection of carbapenem resistant Pseudomonas aeruginosa

Pseudomonas aeruginosa (P. aeruginosa) is an important bacterium that causes many opportunistic hospital-acquired infections. Carbapenems are the first-line treatment for P. aeruginosa infections. Resistance to carbapenem is attributed to the production of carbapenemases or other mechanisms such as overexpression of efflux pumps, overproduction of cephalosporins, and mutation in the oprD gene. This study aims to evaluate four phenotypic methods used for the detection of carbapenems-resistant P. aeruginosa (CRPA) isolates. This cross-sectional study was conducted from September 2022 to February 2023. Samples were collected from inpatients with burn wound infections at the burn center in Al-Najaf Governorate, Iraq. 93 P. aeruginosa isolates of 362 samples were subjected to the disk diffusion method (DDM), modified Hodge test (MHT), modified carbapenem inactivation method (mCIM), and simplified carbapenem inhibition method (sCIM) of different phenotypic methods for detection of CRPA isolates compared to the VITEK^®2 Compact systems (VITEK) that was used as a standard method. Both the DDM and the mCIM methods were almost similar in results. The DDM showed high specificity of 98.3%, a sensitivity of 94.3%, and an accuracy of 96.8%. The mCIM one showed a sensitivity of 94.3%, a specificity of 96.5%, and an accuracy of 95.7%. While the sensitivity of the sMIC method was 85.7%, and specificity 96.6%, and accuracy 92.5%. In comparison with the other phenotypic methods under study, the MHT method showed a low sensitivity of 80%, specificity of 94.8%, and accuracy of 89.3%. The VITEK is very sensitive to the detection of CRPA. Due to the high cost and limited availability of the VITEK, not all labs will probably be able to carry it out in a practical sense. The use of simple phenotypic techniques like DDT, mCIM, and sCIM will be an essential step toward the implementation of large-scale monitoring of these newly discovered resistance determinants. Early diagnosis of CRPA may assist prevent improper use of antimicrobial medication and may also help prevent the growth and spread of these strains. As a result, the identification of carbapenemases producers must be made a regular part of the process.