The Modified Carbapenem Inactivation Method (mCIM): Highly sensitive and specific low-cost tool to assess carbapenemase-producing and non-producing in Gram-negative bacilli

Abstract

Introduction: Carbapenemase-producing Gram-negative bacilli is a worldwide problem, which represent a health concern, because most of its resistance mechanisms are encoded by plasmids, therefore easily transmissible in hospital settings. Many methods have been proposed to detect such resistance, but screening is still challenging, recently the modified carbapenem inactivation method has shown promising results, however more studies need to be performed. Hence, this study aimed to evaluate the performance of the mCIM in carbapenem-resistant Enterobacteriaceae and nonfermenting Gram-negative bacilli isolates.
 Materials and methods: From a microbial collection with molecular characterization of carbapenemase genes previously conducted, 100 Gram-negative bacilli isolates were selected, fifty-two non-carbapenemase producing and 48 carbapenemase-producing isolates. The mCIM was performed according to the CLSI guidelines, and to assess the validity of the method sensitivity and specificity were calculated.
 Results: The sensitivity of the mCIM observed in this study was 96% (46/48) and the specificity was 96,2% (50/52). Most of the Gram-negative bacilli carrying a carbapenemase gene were mCIM-positive, moreover, in carbapenem-resistant isolates that do not produce a carbapenemase (Enterobacteriaceae and non-fermenters) the results of the mCIM were negatives.
 Conclusion: Overall the mCIM provides a low-cost alternative for the screening of carbapenemase-producing Gram-negative bacilli. Our findings highlight that mCIM is a sensitive and specific method to assess carbapenemase-producing in Gram negative bacilli non-fermenters and Enterobacteriaceae as Enterobacter cloacae.