Use of Ertapenem as a Marker for Detection of Carbapenem Resistance for Enterobacteriaceae

Abstract

Introduction: Detection of carbapenem resistance in the clinical microbiology laboratory is challenging. Production of carbapenemase enzymes remains the most important mechanism among Carbapenem Resistant Enterobacteriaceae (CRE). Ertapenem has been found as a sensitive marker for detecting CRE, especially the non-carbapenemase producing CRE. However, limited literature is available discussing its specificity and sensitivity in comparison to gold standard tests. Aim: To compare the ability of the ertapenem disc diffusion test with other confirmatory tests i.e., Epsilometer test (E test), Carbapenemase Nordmann-Poirel (CNP) test, and Polymerase Chain Reaction (PCR) for CRE identification. Materials and Methods: Seventy six phenotypically confirmed Enterobacteriaceae isolates were tested for carbapenem resistance. Ertapenem susceptibility was compared with imipenem, meropenem, and doripenem disc individually and in combination to determine its sensitivity. Further, it was compared with the E test, CNP test, and PCR to find the concordance of the result. Data were analysed by statistical software using Chi-square test with p-value <0.05 as significant. Results: Ertapenem disc independently was able to detect maximum resistant isolates (64/76) in comparison to other individual carbapenem discs or their combinations. Among the four carbapenem discs, the result of the ertapenem disc showed maximum concordance with its corresponding E test. The sensitivity, specificity, Positive Predictive Value (PPV), and Negative Predictive Value (NPV) of the Ertapenem disc compared to the gold standard tests (CNP and PCR) were 89.7%, 62.5%, 95.3%, and 41.7%, respectively. Conclusion: Disc diffusion test using ertapenem disc was observed as a sensitive marker for detecting CRE. The result of the ertapenem disc diffusion test was observed less discordant with E test, CNP test, and PCR in comparison to other carbapenem discs.