Comparison of the Performance of Phenotypic Methods for the Detection of Carbapenem-Resistant Enterobacteriaceae (CRE) in Clinical Practice

Abstract

In order to investigate the diagnostic performance characteristics of four phenotypic assays in detecting carbapenem-resistant Enterobacteriaceae (CRE), we collected the CRE strains from infected patients. The results of carbapenemase gene detection, blaKPC-2, blaOXA-23, blaNDM-1, blaNDM-4, blaNDM-5, blaIMP-4, and blaIMP-8, were used as a standard to evaluate the performances of combined disk test (CDT), modified carbapenem inactivation method(mCIM)/EDTA-modified carbapenem inactivation method(eCIM), NG-Test CARBA 5 (CARBA), and color developing immunoassay (CDI). The compliance of phenotype results based on CDT, mCIM/eCIM, CARBA, and CDI with genetic detection results was 94% (231/247), 95% (235/247), 98% (242/247), and 99% (246/247), respectively. CDT demonstrated a low specificity for carbapenemase detection, low negative predictive value (NPV), and low sensitivity for metallo-β-lactamase (79%, 55%, and 88%, respectively); it also failed to accurately detect IMP. The mCIM/eCIM assay had serious problems in detecting OXA-23-like carbapenemases. The sensitivity and specificity of CARBA and CDI were higher than those of the first two methods. However, CARBA did not cover the detection of OXA-23, while CDI cannot detect IMP-8, resulting in low NPVs (70% and 88%, respectively). In conclusion, CARBA and CDI assays are highly accurate except individual rare genes and allow direct genotype detections. CDT and mCIM/eCIM assays are moderately accurate and can only distinguish serine-β-lactamases from metallo-β-lactamases. Laboratories should choose the appropriate method that meets their needs based on its characteristic.

Insights on the performance of phenotypic tests versus genotypic tests for the detection of carbapenemase-producing Gram-negative bacilli in resource-limited settings

“…1 The antibiogram analysis of Carbapenemase-producing Gram-negative (CPGN) pathogens (n = 71) including, Enterobacterales and non-glucosefermenting Gram-negative bacilli (GNB) against various classes of antimicrobial agents low NPV in detecting CPE (74%, 12.50%) and CP-NF (62.16%, 17.64%), respectively. Such finding could be attributed to failure of MHT to detect 21 CPO isolates (7 CPE and 14 CP-NFB) that carry bla KPC either alone or in combination with bla OXA−48 [1,14]. However, Yan et al had improved the efficiency of the MHT in detecting KPC-producing K. pneumoniae mucoid colonies by using EDTA that primarily lyses bacterial cells to release β-lactamases [35].…”

“…Carbapenemases are β-lactamases produced by carbapenem-resistant (CR) bacteria as their major antimicrobial-resistance mechanisms [1,2]. Owing to their broad spectrum of activity and stability towards the majority of β-lactamases, carbapenems are considered one of the last lines of therapy to treat severe infections caused by multi-drug resistant (MDR) bacteria [2].…”

“…Generally, mechanisms contributing to CR could be through overexpression of efflux pump, decrease in outer membrane permeability coupled with hyper-production of AmpC β-lactamases, and finally through the production of carbapenemase enzymes as the most predominant resistance mechanism [1,5]. Carbapenemases are β-lactamases that belong to different Ambler classes (A, B, and D).…”

“…To overcome these challenges, several simple and affordable phenotypic tests were recommended by clinical and laboratory standard institute (CLSI) that allow effective detection of CPOs particularly, CPGN pathogens. Currently, growth-based assays and colorimetric hydrolysis methods (blue carba test: BCT, Carba Nordmann/ Poirel: Carb NP) that depends on the growth of the organism in presence of carbapenem antibiotics and degradation of carbapenem products, respectively are commonly used in clinical practice [1,7,14]. Of note, CLSI had archived MHT, while other methods as mCIM and Carba NP were endorsed.…”

“…These urges evaluating and regular updates on the sensitivity/specificity values of the existed phenotypic and genotypic diagnostic methods of the most common circulating CPGN pathogens. Although, the phenotypic detection and molecular characterization of CPGN pathogens had been previously reported in literature [13][14][15][16], still more studies are urgently required to validate the laboratory performance (sensitivity/specificity/positive predictive value/negative predictive value) of the respective phenotypic methods and to correlate them with the different types of carbapenemase enzymes [1,14]. Therefore, in this study we aimed to evaluate the performance of four major phenotypic approaches namely MHT, mCIM, BCT, combined disk test by EDTA (CDT) for detecting CPGN pathogens.…”