Comparison of the VITEK Gram-Negative Identification Card and an enhanced version for identification of Salmonella, Escherichia coli, and other Enterobacteriaceae: method modification.

The VITEK Gram-Negative Identification Card (GNI) was compared to an enhanced version of the test kit, the GNI + Card. The GNI Card is an official AOAC method (991.13) for identification of Salmonella, Escherichia coli, and other Enterobacteriaceae in foods. In this comparison 5 replicates of 124 gram-negative stock culture strains were evaluated to determine equivalency. Isolates were obtained primarily from food sources, with 108 of the isolates representing 15 genera within the family Enterobacteriaceae. Overall agreement between the GNI Card and the GNI + Card was 98.2%. Of the 23 strains of Salmonella tested, the longest identification time for the GNI Card was 10 h, with 43.5% of the strains identifying in 4 h or less. The longest identification time of the same Salmonella strains tested with the GNI + Card was 8 h, with 95.7% of the strains identifying within 4 h. The GNI + Card provided increased speed of identification while retaining the accuracy of the GNI Card. The GNI method for identifying Salmonella, Escherichia coli, and other Enterobacteriaceae was approved as a method modification by AOAC INTERNATIONAL.