Evaluate the Modified Carbapenem Inactivation Method for Phenotypic Detection of Carbapenemase Production Among Gram-Negative Bacteria

Global growing infections by multi-drug resistance (MDR) or extensively drug-resistant (XDR) bacteria are a serious public health problem which can increase the rate of mortality and morbidity even in children. Carbapenem is the last choice therapy in case of antibiotic-resistant bacteria presence.

This study aimed to evaluate the easy to use method to identify carbapenemase producing bacteria which include in CLSI.

In this descriptive study, 125 carbapenem-resistant and 97 carbapenem-susceptible gram-negative bacteria were included. PCR was used to identify carbapenemase enzymes include VIM, IMP, KPC, NDM-1, SPM-1, OXA-48 as a gold standard method. The modified carbapenem inactivation method (mCIM) was employed to phenotypically identify carbapenemase-producing bacteria. Some modifications were made to the CLSI proposed mCIM to ensure more accurate results in contrast of PCR.

The OXA-48 is the most prevalent detected carbapenemase and SPM-1 was not detected in any of strain. The results of the mCIM according to CLSI guide line demonstrated 100% sensitivity to define carbapenemase-producing bacteria. However, in the cases of non-carbapenemase-producing bacteria, only 4% of mCIM test results were consistent with the outcome of PCR. Decrease of the incubation time and the consider 15mm as a break point could increase the accuracy of mCIM against PCR.

The results of this study endorse that mCIM test is a valuable method to detect carbapenemase producing bacteria if the three hours consider instead of 4 hours with 15mm break point.