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

Abstract

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 Enterobacteriaceae, 73 Acinetobacter baumannii, and 158 Pseudomonas aeruginosa 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 Enterobacteriaceae strains, 147 expressed the carbapenemase genes blaKPC−2 (58.5%), blaIMP−4 (21.8%), blaIMP−2 (2.0%), blaVIM−1 (6.1%), blaNDM−1 (10.2%), and blaOXA−48 (1.4%). sCIM results had high concordance with PCR results (99.5%) and mCIM results (100%) with the exception of one Klebsiella pneumoniae strain, which had an minimal inhibitory concentration (MIC) for imipenem of 0.25 mg/L. PCR demonstrated that 53 of the 73 A. baumannii isolates expressed the carbapenemase genes blaOXA−23 (98.1%) and blaVIM−2 (1.8%). sCIM and PCR results corresponded but all A. baumannii isolates were carbapenemase negative by the mCIM. PCR demonstrated that 25 of the 158 P. aeruginosa isolates expressed carbapenemase genes blaVIM−1 (52%), blaVIM−2 (8%), blaVIM−4 (36%), and blaIMP−4 (4%). sCIM results had high concordance with PCR results (100%) and the mCIM results (99.4%) with the exception of one P. aeruginosa isolate that expressed the blaVIM−4 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.

The Rapid Carbapenemase Detection Method (rCDM) for Rapid and Accurate Detection of Carbapenemase-Producing Enterobacteriaceae and Pseudomonas aeruginosa

“…All strains were identified at the species level using MALDI-TOF MS (Bruker Daltonics, Bremen, Germany) and a Vitek 2 compact instrument (bioMérieux, Hazelwood, MO, USA). Carbapenemase genes were detected in these strains using PCR and sequencing as previously described (Jing et al, 2018). Minimum inhibitory concentration (MIC) of imipenem was determined using broth microdilution method.…”

“…A zone of inhibition ≥26 mm was considered a negative result. A zone of inhibition 23–25 mm was considered an inconclusive result (Jing et al, 2018).…”

“…However, these procedures are lengthy (mCIM and eCIM require 24 h to detection), require expensive equipment such as MALDI-TOF MS, or involve reagents that cannot be stored for long periods of time (Carba NP, CarbaNP solution B can be stored in solution at 4–8°C for up to 3 days) (Burckhardt and Zimmermann, 2011; CLSI, 2018). In 2018, we improved on the mCIM method with the simplified carbapenem inactivation method (sCIM) (Jing et al, 2018). sCIM is easy to operate and the results are easy to observe; however, this method still takes 16–24 h to observe the results (Jing et al, 2018).…”

“…In 2018, we improved on the mCIM method with the simplified carbapenem inactivation method (sCIM) (Jing et al, 2018). sCIM is easy to operate and the results are easy to observe; however, this method still takes 16–24 h to observe the results (Jing et al, 2018). In order to detect carbapenemase-producing strains in a shorter time, we have designed a new detection method, the rapid carbapenemase detection method (rCDM), that can detect carbapenemase-producing Enterobacteriaceae and Pseudomonas aeruginosa within 5–6 h based on antimicrobial disk susceptibility tests, and compared it with sCIM.…”

Comparative Study of CDST & Multiplex PCR to Detect MBL Producing Gram-Negative Bacilli among VAP Patients Admitted in a Public Medical College Hospital of Bangladesh

“…The media used was Mueller–Hinton Agar Media, the potency of the imipenem disc was 10 µg. The standard values determined by the National Committee for Clinical Laboratory Standards (NCCLS) pathogens were classified as sensitive (21 mm), intermediate resistant (16–20 mm), and resistant (15 mm) [27,28] and a zone of inhibition of ≥20 mm was considered sensitive, a zone of inhibition less than 20 mm was considered resistant to Imipenem [29]. All the imipenem-resistant Pseudomonas, E. coli, Klebsiella , and Acinetobacter , were tested for detection of MBLs by Imipenem-EDTA CDST.…”