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

Background: 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.Objectives: This study aimed to evaluate the easy to use method to identify carbapenemase producing bacteria which include in CLSI. Methods: 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.Results: 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.Conclusions: 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.

Automated summary

This study evaluated an easy to use method to identify carbapenemase producing bacteria and improved its accuracy through modifications. The results showed high sensitivity in identifying carbapenemase-producing bacteria, but low accuracy in non-carbapenemase-producing bacteria. The use of modified incubation time and breakpoint can enhance the accuracy of this method against PCR.