4. AOACRIMicroMethods-2018Awards

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FOOD BIOLOGICAL CONTAMINANTS

Evaluation of the VITEK ® 2 Gram Positive (GP) Microbial Identification Test Card: Collaborative Study E rin C rowley , P atrick B ird , K iel F isher , K atherine G oetz , M egan B oyle , M. J oseph B enzinger , J r , M arc J uenger , J ames A gin , and D avid G oins Q Laboratories, Inc., 1400 Harrison Ave, Cincinnati, OH 45214 R onald L. J ohnson 1 bioMérieux, Inc., 595 Anglum Rd, Hazelwood, MO 63042 Collaborators: J. Canale, D. Cherney, M. Coakley, J. Colón-Reveles, J. Crowe, R. Daugherty, P. Dombroski, H.P. Dwivedi, J. Dyer, C. Elems, J. Finnigan, G. Fraser, A. Garza, J. Glover, P. Hanson, M. Hayman, E. High, L. Johnson, M. Kelly, S. Kim, S.G. Kim, M. Kingsley, M. McDonough, A. Miller, J. Mills, S. Montez, M.A. Murphy, G. Parra, U. Patel, L. Robertson, S. Robeson, J. Ruebl, A. Saldana, Y. Salfinger, M. Segarra, B. Shaw, T. Sidebottom, D. Toney, H. Wang, P. Wikoff, K. Wilson

present in raw materials, production environments, and finished products. The technology of the VITEK 2 system enables fast identification, within hours rather than the days required for classical methods (2). Gram-positive organism identification is achieved through the use of the Gram Positive (GP) Identification Card. This card is intended to be used with the VITEK 2 system for the automated identification of most significant Gram-positive organisms. The GP card is a single- use disposable and is based on established biochemical methods and newly developed substrates measuring carbon source utilization, resistance, and enzymatic activities. There are 43 biochemical tests and one negative control well within each GP card. Identification results are available in approximately 8 h or less (3). The identification of the test organism is based on the data and knowledge about the organism and reactions being analyzed. As part of the identification process, the VITEK 2 software compares the test set of reactions to the expected set of reactions of each organism. A qualitative value, referred to as the percent probability of the identification result, is calculated and reported alongside the identification result. This value relates to how well the observed reactions compare to the typical reactions of each organism (4). The VITEK 2 GP test method was validated according to AOAC guidelines for Performance Tested Method SM (PTM) and Official Method SM (OMA) precollaborative studies for the identification of Listeria and Staphylococcus species (5). In the combined contract laboratory andAOAC independent laboratory studies, 63 inclusivity strains representing seven Listeria species and four Staphylococcal species claims ( Listeria grayi, Listeria innocua, Listeria ivanovii ssp. Ivanovii, Listeria ivanovii ssp. Londoniensis, Listeria monocytogenes, Listeria seeligeri, Listeria welshimeri, Staphylococcus hyicus, Staphylococcus intermedius, Staphylococcus aureus, and Staphylococcus epidermidis ) from the VITEK 2 GP database and 40 exclusivity strains were challenged for correct identification. All test strains were tested from three recommended culture media: Trypticase soy agar (TSA), Columbia agar with 5% sheep blood (CBA), and Trypticase soy agar plates with 5% sheep blood (TSAB) at 12 and 48 h of incubation. Overall percent correct identifications in the combined internal and independent studies from 12 h TSA, CBA, and TSAB cultures were 98, 97, and 98%, respectively. Overall correct identifications in the combined internal and independent studies for all test strains from 48 h TSA, CBA,

Submitted for publication March 1, 2012. The recommendation was approved by the Methods Committee on Microbiology as First Action. See “Standards News,” (2012) Inside Laboratory Management , March/April issue. 1  Corresponding author’s e-mail: ron.johnson@biomerieux.com DOI: 10.5740/jaoacint.CS2012_02 bacteria often rely on time-consuming growth in culture media, followed by isolation, biochemical identification, and sometimes serology (1). The VITEK 2 ® system addresses this need by providing automated testing to identify microorganisms A collaborative study was conducted to evaluate the performance of the VITEK ® 2 Gram Positive (GP) identification card for use with the VITEK 2 automated microbial identification system. The GP test card is used in the identification of selected Gram positive organisms, including Listeria and Staphylococcus species. The VITEK 2 GP card is based on 43 biochemical tests measuring carbon source utilization, inhibition and resistance, and enzymatic activities. A total of 20 laboratories representing government, industry, and private testing laboratories throughout the United States participated. In this study, 720 Gram-positive inclusivity isolates were analyzed by the GP Identification method. Of the 720 well-characterized isolates, 714 were identified correctly, zero were misidentified, zero were unidentified, and six were not characterized as a Gram-positive organism by the VITEK 2 GP method. Additionally, 120 strains exclusive of Gram-positive organisms were screened by Gram stain. A total of 106 isolates were correctly excluded. Fourteen organisms were incorrectly characterized by Gram stain procedures, thus resulting in improper analysis and misidentification by VITEK GP. The VITEK 2 GP identification method is an acceptable automated method for the rapid identification of selected Gram-positive bacteria. T he rapid and accurate identification of foodborne organisms is a critical component for ensuring the safety of consumers. Traditional methods to detect foodborne

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