Phenotypic Detection of Carbapenemase-Producing Enterobacteriaceae by Use of Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry and the Carba NP Test

Abstract

f We compared the diagnostic accuracy of the Carba NP test with that of a straightforward matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) method for detecting carbapenemase-producing Enterobacteriaceae (CPE). Using PCR as the reference method, both tests demonstrated a sensitivity of 87% and a specificity of 100%. MALDI-TOF MS offers a potential alternative for the rapid detection of CPE in the clinical laboratory setting. The global spread of carbapenemase-producing Enterobacteriaceae (CPE) is a major threat to public health (1). The efficient laboratory detection of these agents requires a rapid phenotypic test that provides accurate results while awaiting confirmation by PCR. In this study, a method was developed for detecting CPE using an imipenem hydrolysis assay and matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS), using the Vitek MS research use only (RUO) system (bioMérieux, Marcy l'Étoile, France). Using PCR as a reference method, the diagnostic accuracy of MALDI-TOF MS was compared with that of the Carba NP test (CNP).The investigation was conducted at Melbourne Pathology and Swinburne University of Technology, Melbourne, Australia, between October 2013 and April 2014. A panel of 105 genetically characterized Enterobacteriaceae was assembled from nine Australian laboratories. All strains were identified by MALDI-TOF MS (Vitek MS [bioMérieux]) using the Vitek MS Database version 2.0 (bioMérieux) and had MICs for meropenem determined by Etest (bioMérieux). Molecular characterization had been performed by various methods (2-11); at a minimum, each strain had been subjected to PCR, including targets for bla KPC , bla NDM , bla IMP , bla VIM , and bla OXA-48 (2-11). The entire collection was assembled prior to the study, and all of the strains obtained were included.The CNP was performed according to a previously published method (12) on strains cultured on Columbia blood agar (CBA) for 18 to 24 h. The results were read by a microbiologist who was blinded to all other results in the study.The MALDI-TOF MS method was adapted from a previous

Carba NP Test as a Rapid Diagnostic Tool for Carbapenemase Producers

“…Our results showed slight difference from those of Knox and his colleagues (2014) in Australia who evaluated the performance of Carba NP test in detecting carbapenemase production by Enterobacteriaceae in comparison to PCR and found that the sensitivity and specificity of the Carba NP test were (40/46) 87% and (59/59) 100% respectively (19) .…”

MALDI-TOF MS detection of carbapenemase activity in clinical isolates of Enterobacteriaceae spp., Pseudomonas aeruginosa, and Acinetobacter baumannii compared against the Carba-NP assay

“…inexpensive test to detect carbapenemase activity (Nordmann et al, 2012b;Dortet et al, 2012), but the use of MALDI-TOF MS for carbapenemase detection has been increasing (Hrabak et al, 2011(Hrabak et al, , 2012Kempf et al, 2012;Wang et al, 2013;Sauget et al, 2014;Johansson et al, 2014;Hoyos-Mallecot et al, 2014;Nagy et al, 2014;Knox et al, 2014;Hrabak, 2015). In this report, we used MALDI-TOF MS analysis to detect carbapenemase activity in a diverse panel of clinical isolates of Enterobacteriaceae spp., P. aeruginosa and A. baumannii that collectively express one of eight different carbapenemases, and compared the results against the use of the Carba-NP assay on selected isolates.…”

Detection of carbapenemase activity using VITEK MS: interplay of carbapenemase type and period of incubation

“…Most studies have evaluated ertapenem hydrolysis by testing the Microflex LT instrument (Bruker Daltonics) (Carvalhaes et al, 2013). To the best of our knowledge, only one recently published study evaluated the detection of carbapenemase activity by using the VITEK MS instrument (bioMérieux) (Knox et al, 2014). The authors reported a lack of sensitivity (87 %) by testing imipenem as substrate.…”