Evaluation of two new commercial immunochromatographic assays for the rapid detection of OXA-48 and KPC carbapenemases from cultured bacteria

Abstract

Background: Rapid detection and confirmation of carbapenemases remains very challenging for diagnostic laboratories. Objectives: The objective of this study was to assess the performance of two new immunochromatographic (IC) commercial assays for the rapid detection of OXA-48-producing and KPC-producing Enterobacteriaceae in pure bacterial isolates. Methods: A panel of 92 bacterial isolates predominantly including carbapenem-non-susceptible Enterobacteriaceae with previously defined carbapenem resistance mechanisms was tested. Then, 342 consecutive carbapenemnon-susceptible Enterobacteriaceae isolates referred to the reference laboratory were investigated prospectively in parallel with other phenotypic tests and with multiplex PCR and sequencing as the gold standard. Results: In the collection panel, each of the two IC assays correctly detected all 30 OXA-48-like-producing isolates and 25 KPC-producing isolates, whatever the species, their association with other b-lactamases and the level of resistance to carbapenems. All other carbapenemase producers and all non-carbapenemase-producing isolates yielded negative resultswith both tests. In the prospective evaluation, all OXA-48-like-producing Enterobacteriaceae isolates (n=130) and KPC-producing Enterobacteriaceae isolates (n=33)were correctly detected by the individual IC assays, while 179 non-OXA-48-like-producing and non-KPC-producing strains (137 non-carbapenemase producers and 42 isolates belonging to other carbapenemase family types) yielded negative results. Thus, each assay yielded 100% sensitivity and 100% specificity for the detection of OXA-48-like or KPC enzymes, respectively, at 15 min. Conclusions: The two IC assays allow rapid and reliable direct confirmation of OXA-48 and KPC carbapenemases fromculture colonies and appear to be very useful additions to the existing tests, obviating the need formore costly characterization by molecular amplification methods.