Performance of Vitek 2 for Antimicrobial Susceptibility Testing of Enterobacteriaceae with Vitek 2 (2009 FDA) and 2014 CLSI Breakpoints

Abstract

Vitek 2 (bioMérieux Inc., Durham, NC) is a widely used commercial antimicrobial susceptibility test system. We compared the MIC results obtained using the Vitek 2 AST-GN69 and AST-XN06 cards to those obtained by CLSI broth microdilution (BMD) for 255 isolates of Enterobacteriaceae, including 25 isolates of carbapenem-resistant Enterobacteriaceae. In total, 25 antimicrobial agents were examined. For 10 agents, the MIC data were evaluated using two sets of breakpoints: (i) the Vitek 2 breakpoints, which utilized the 2009 FDA breakpoints at the time of the study and are equivalent to the 2009 CLSI M100-S19 breakpoints, and (ii) the 2014 CLSI M100-S24 breakpoints. There was an overall 98.7% essential agreement (EA). The categorical agreement was 95.5% (CA) using the Vitek 2 breakpoints and 95.7% using the CLSI breakpoints. There was 1 very major error (VME) (0.05%) observed using the Vitek 2 breakpoints (cefazolin) and 8 VMEs (0.5%) using the CLSI breakpoints (2 each for aztreonam, cefepime, and ceftriaxone, and 1 for cefazolin and ceftazidime). Fifteen major errors (MEs) (0.4%) were noted using the Vitek 2 breakpoints and 8 (0.5%) using the CLSI breakpoints. Overall, the Vitek 2 performance was comparable to that of BMD for testing a limited number of Enterobacteriaceae commonly isolated by clinical laboratories. Ongoing studies are warranted to assess performance in isolates with emerging resistance. Most clinical laboratories in the United States use commercial automated systems for antimicrobial susceptibility testing (AST). The failure of these systems to detect resistance in Enterobacteriaceae, in particular the ␤-lactam resistance mediated by emerging resistance mechanisms, has been reported in several studies (1-3). Specifically, Vitek 2 (bioMérieux, Inc., Durham, NC) performed poorly compared to broth microdilution (BMD) and disk diffusion for detecting cefepime (2), meropenem (1, 3), and imipenem resistance (1) in Klebsiella pneumoniae isolates harboring the bla KPC gene. False-susceptible piperacillin-tazobactam results were obtained with Vitek 2 when testing Escherichia coli isolates expressing a variety of extended-spectrum ␤-lactamases (ESBLs), in particular, CTX-M-15 (4). In 2010, bioMérieux voluntarily recalled AST cards containing piperacillin-tazobactam after confirming user-reported false-susceptible and false-resistant errors for E. coli. This recall was expanded in 2011 to include piperacillin-tazobactam testing for K. pneumoniae, Morganella morganii, Proteus mirabilis, Proteus vulgaris, Providencia rettgeri, Providencia stuartii, Pseudomonas aeruginosa, and Salmonella enterica (http://www.fda.gov/Safety/MedWatch/SafetyInformation /SafetyAlertsforHumanMedicalProducts/ucm233405.htm). bioMérieux has since introduced new U.S. Food and Drug Administration (FDA)-cleared AST cards with reformulated piperacillin-tazobactam and imipenem, as well as revised software intended to improve the performance with these antimicrobials.In addition to the challenge that manufacturers of commercial AST systems have...

Commentary: Continuing Challenges for the Clinical Laboratory for Detection of Carbapenem-Resistant Enterobacteriaceae

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