Poster Presentation Australian Society for Microbiology Annual Scientific Meeting 2014

Phenotypic detection of carbapenemase-producing Enterobacteriaceae using MALDI-TOF MS and the Carba NP test (#324)

James Knox 1 , Snehal Jadhav 2 , Danielle Sevior 3 , Alex Agyekum 4 , Margaret Whipp 5 , Lynette Waring 1 , Jonathan Iredell 4 , Enzo Palombo 2
  1. Melbourne Pathology, Melbourne, Victoria, Australia
  2. Swinburne University of Technology, Melbourne, Victoria, Australia
  3. Biomerieux, Melbourne, Victoria, Australia
  4. Institute for Clinical Pathology and Medical Research, Westmead, Sydney, New South Wales, Australia
  5. Microbiological Diagnostic Unit, Public Health Laboratory, University of Melbourne, Melbourne, Victoria, Australia

Introduction: A simple method for the detection of carbapenemase-producing Enterobacteriaceae (CPE) by matrix-assisted laser desorption ionisation-time of flight mass spectrometry (MALDI-TOF MS) using VITEK MS RUO (bioMérieux, Marcy l’Etoile, France) was developed for routine use in the clinical laboratory. The diagnostic accuracy of this approach was compared with the Carba NP test.

Methods: A collection of molecularly-characterised Enterobacteriaceae comprising 46 carbapenemase-producing strains and 59 non-carbapenemase-producing strains were tested using an imipenem hydrolysis assay and MALDI-TOF MS. Each strain was also subjected to the Carba NP test.

Results: Among meropenem-resistant strains of Enterobacteriaceae the MALDI-TOF MS method demonstrated a sensitivity of 97% and a specificity of 100%, and the Carba NP test had a sensitivity of 91% and specificity of 100% (p = 0.61). When meropenem-intermediate and susceptible strains were included, both tests had a sensitivity and specificity of 87% and 100%, respectively (p = 1). MALDI-TOF MS detected all four OXA-48 producing strains in the collection, by comparison the Carba NP test identified only one (p = 0.14).

Conclusion: Both the Carba NP test and MALDI-TOF MS performed well for carbapenem-resistant Enterobacteriaceae. MALDI-TOF MS offers a potential alternative method for detection of CPE in the clinical laboratory.