Performance of chromID® CARBA-SMART medium and carbapenemase inhibition method for the detection of carbapenemases among Gram negative bacilli

Abstract

Background:Early detection of carbapenemase enzymes among Gram negative bacilli (GNB) is mandatory to prevent their spread. Objective: The goal of this study was to evaluate the performance of chromID® CARBA-SMART medium and carbapenemase inhibition method (CIM) for detection of carbapenemases in GNB. Methodology: A total of 142 GNB isolates were collected and tested using Vitek-2® system for identification and antimicrobial susceptibility testing The carbapenem resistant (CR) GNB were tested for carbapenemase production by phenotypic methods; chromID® CARBA-SMART medium and CIM. Carbapenemase genes (𝑏𝑙𝑎NDM-1, blaSIM-1,𝑏𝑙𝑎VIM-2, 𝑏𝑙𝑎KPC-1, blaGIM-1, blaSPM-1 and 𝑏𝑙𝑎OXA-48) were detected by PCR. Results: By minimal inhibitory concentration (MIC), 111 (78.17 %) of the 142 isolates were shown to be carbapenem resistant. Sensitivity and specificity of CIM and ChromID® CARBA-SMART medium were (100% and 66.7% respectively) for CIM and (86.7% and 100% respectively) for the medium. Resistance to carbapenem was associated with high percentages of resistance to many antibiotic classes. Carbapenemase genes were detected in 82% (91/111) of CR GNB with 𝑏𝑙𝑎NDM-1 (58.6%) and 𝑏𝑙𝑎OXA-48 (55.9 %) having the highest prevalence, followed by 𝑏𝑙𝑎KPC-1 (36 %) then 𝑏𝑙𝑎VIM-2 (10.8%) and lastly blaSPM-1 (3.6 %) and blaSIM-1 (1.8 %). The blaGIM-1 gene was not detected in any isolate. Conclusion: Carbapenemase inhibition method was found to be a very sensitive, easy, and cheap test for carbapenemase detection but needs the addition of ChromID® CARBA-SMART medium to improve the specificity of the test. This study has a high prevalence of carbapenemases among isolates with potential of rapid spread necessitating need for phenotypic tests.

Keywords

• carbapenemase
• inhibition
• genes