The Simplified Carbapenem Inactivation Method (sCIM) for Simple and Accurate Detection of Carbapenemase-Producing Gram-Negative Bacilli.

This study reports the simplified carbapenem inactivation method (sCIM) to detect carbapenemase-producing gram-negative bacilli in a simple and accurate manner. This method is based on the modified carbapenem inactivation method (mCIM) with the improvement of experimental procedures. Instead of incubating the antibiotic disk in the organism culture media, the organism to be tested was smeared directly onto the antibiotic disk in the sCIM. For evaluating the sensitivity and specificity of the method, a total of 196 , 73 , and 158 isolates were collected. Polymerase chain reaction (PCR) was used to detect the carbapenemase genes. Phenotypic evaluations were performed using both the sCIM and the mCIM. PCR results showed that, of the 196 strains, 147 expressed the carbapenemase genes (58.5%), (21.8%), (2.0%), (6.1%), (10.2%), and (1.4%). sCIM results had high concordance with PCR results (99.5%) and mCIM results (100%) with the exception of one strain, which had an minimal inhibitory concentration (MIC) for imipenem of 0.25 mg/L. PCR demonstrated that 53 of the 73 isolates expressed the carbapenemase genes (98.1%) and (1.8%). sCIM and PCR results corresponded but all isolates were carbapenemase negative by the mCIM. PCR demonstrated that 25 of the 158 isolates expressed carbapenemase genes (52%) (8%) (36%), and (4%). sCIM results had high concordance with PCR results (100%) and the mCIM results (99.4%) with the exception of one isolate that expressed the gene. The sCIM offers specificity and sensitivity comparable to PCR but has the advantage of being more user-friendly. This method is suitable for routine use in most clinical microbiology laboratories for the detection of carbapenemase-producing gram-negative bacilli.