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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.

A collaborative study was conducted to evaluate the performance of the VITEK 2 Gram-negative (GN) Identification card for use with the VITEK 2 automated microbial identification system. The GN test card is used in the identification of fermenting and nonfermenting Gram-negative bacilli, including the select agent organisms Brucella melitensis, Francisella tularensis, Burkholderia mallei, B. pseudomallei, and Yersinia pestis. The VITEK 2 GN card is based on 47 biochemical tests measuring carbon source utilization, inhibition and resistance, and enzymatic activities. A total of 20 laboratories representing government, industry, and private testing facilities throughout the United States participated. In this study, 720 Gram-negative inclusivity isolates were analyzed by the GN Identification method. Of the 720 well-characterized isolates, 707 were identified correctly, 0 were misidentified, 0 were unidentified, and 13 were not characterized as a Gram-negative organism. Additionally, 120 isolates exclusive of fermenting and nonfermenting Gram-negative bacilli were screened by Gram stain. A total of 117 isolates were correctly excluded. Three organisms were incorrectly characterized by Gram stain procedures, resulting in incorrect analysis and misidentification by VITEK 2 GN. The VITEK 2 GN identification method is an acceptable automated method for the rapid identification of Gram-negative bacteria.

The 3M Molecular Detection Assay (MDA) Salmonella is used with the 3M Molecular Detection System for the detection of Salmonella spp. in food, food-related, and environmental samples after enrichment. The assay utilizes loop-mediated isothermal amplification to rapidly amplify Salmonella target DNA with high specificity and sensitivity, combined with bioluminescence to detect the amplification. The 3M MDA Salmonella method was compared using an unpaired study design in a multilaboratory collaborative study to the U.S. Department of Agriculture/Food Safety and Inspection Service-Microbiology Laboratory Guidebook (USDA/FSIS-MLG 4.05), Isolation and Identification of Salmonella from Meat, Poultry, Pasteurized Egg and Catfish Products for raw ground beef and the U.S. Food and Drug Administration/Bacteriological Analytical Manual (FDA/BAM) Chapter 5 Salmonella reference method for wet dog food following the current AOAC guidelines. A total of 20 laboratories participated. For the 3M MDA Salmonella method, raw ground beef was analyzed using 25 g test portions, and wet dog food was analyzed using 375 g test portions. For the reference methods, 25 g test portions of each matrix were analyzed. Each matrix was artificially contaminated with Salmonella at three inoculation levels: an uninoculated control level (0 CFU/test portion), a low inoculum level (0.2-2 CFU/test portion), and a high inoculum level (2-5 CFU/test portion). In this study, 1512 unpaired replicate samples were analyzed. Statistical analysis was conducted according to the probability of detection (POD). For the low-level raw ground beef test portions, the following dLPOD (difference between the POD of the reference and candidate method) values with 95% confidence intervals were obtained: -0.01 (-0.14, +0.12). For the low-level wet dog food test portions, the following dLPOD with 95% confidence intervals were obtained: -0.04 (-0.16, +0.09). No significant differences were observed in the number of positive samples detected by the 3M MDA Salmonella method versus either the USDA/FSIS-MLG or FDA/BAM methods.

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