Comparison of nine different selective agars for the detection of carbapenemase-producing Enterobacterales (CPE).

The rapid identification of patients colonized with carbapenem-resistant Enterobacterales (CRE) is important for infection control purposes. Here, we compared and evaluated nine different agars for the detection of carbapenemase-producing Enterobacterales (CPE) from clinical samples. In the study, 69 CPE and 40 carbapenemase-negative isolates were included. Overall, seven commercially available screening agars were assessed: Brilliance CRE (Oxoid), Chromatic CRE (Liofilchem), chromID CARBA and chromID OXA-48 (both bioMérieux), three ESBL agars (Chromatic ESBL [Liofilchem], chromID ESBL [bioMérieux], Brilliance ESBL [Oxoid]), and two agars produced in-house (McCARB and McCARB-T). The sensitivity of CRE agars for CPE detection ranged from 34.8 to 98.6%. Brilliance CRE and McCARB/McCARB-T showed the overall highest sensitivity (98.6 and 97.1%, respectively). OXA-48 producers were the most difficult to detect; only 4/9 agars detected all isolates (McCARB/McCARB-T, Chromatic CRE, ChromID OXA-48). Additionally, all ESBL-negative OXA-48 isolates failed to grow on ESBL screening agars. Specificity ranged from 30 (Brilliance ESBL) to 100% (ChromID OXA-48). The limit of detection for different CPE in spiked stool samples ranged from 1.5 × 101 to 1.5 × 103 CFU/ml. Overall, Brilliance CRE and the McCARB in-house agars showed the best performance and were able to detect most CPE, including almost all OXA-48. ESBL agars were not suitable for detection of CPE alone, as OXA-48 isolates negative for ESBL were suppressed. The highest sensitivity was achieved by a combination of a CRE agar and an ESBL agar.

Comparison of Phenotypic Tests and an Immunochromatographic Assay and Development of a New Algorithm for Detection of OXA-48-like Carbapenemases.

OXA-48 is the most prevalent carbapenemase in Enterobacteriaceae in Europe and the Middle East, but it is frequently missed because many isolates display low MICs for carbapenems. Furthermore, in contrast to metallo-ß-lactamases or Klebsiella pneumoniae carbapenemases (KPC), no specific inhibitor is available for the phenotypic detection of OXA-48. Molecular detection of blaOXA-48 is the "gold standard" but is not available in many laboratories. A few phenotypic assays have been described but have not been independently evaluated. The aim of this study was the systematic comparison of phenotypic tests and an immunochromatographic assay (ICT) for the detection of OXA-48/OXA-48-like carbapenemases and the development of an algorithm for reliable phenotypic detection of OXA-48. Four phenotypic tests (temocillin disk test, faropenem disk test, OXA-48 disk test, and high-inoculum [HI] OXA-48 disk test) and a new ICT (OXA-48 K-SeT) were compared by using a set of 166 Enterobacteriaceae isolates, including isolates producing OXA-48/OXA-48-like carbapenemases (n = 84) or Ambler class A and B carbapenemases (n = 41) and carbapenemase-negative isolates (n = 41). The sensitivity and specificity for the different assays were 100% and 43.9% for temocillin, 57.1% and 98.8% for faropenem, 53.6% and 100% for the OXA-48 disk test, 98.8% and 97.6% for the HI OXA-48 disk test, and 100% and 100% for the ICT, respectively. The ICT displayed the highest sensitivity and specificity and was the most rapid assay, but it is more costly than phenotypic assays. Based on these results, a new algorithm incorporating temocillin, faropenem, and ICT which allows cost-effective detection of OXA-48 with 100% sensitivity and specificity was developed.