Multicenter Evaluation of the Vitek 2 Anaerobe and Corynebacterium Identification Card

Abstract

The new anaerobe and Corynebacterium (ANC) identification card for Vitek 2 was compared with a 16S rRNA gene sequencing (16S) reference method for accuracy in the identification of corynebacteria and anaerobic species. Testing was performed on a Vitek 2 XL system with modified software at three clinical trial laboratories. Reproducibility was determined with nine ATCC quality control strains that were tested 20 times over a minimum of 10 days at all three sites. A challenge set of 50 well-characterized strains and 365 recent fresh and frozen clinical isolates were included in the study. The expected positive and negative biochemical well reactions were also evaluated for substrate reproducibility. All strains were tested with the ANC card, and clinical isolates were saved for 16S rRNA gene sequencing. All reproducibility tests yielded expected results within a 95% confidence interval, except for that with Corynebacterium striatum ATCC 6940, for which identification failed at one trial site. For the challenge isolates, there was 98% correct identification, 5% low discrimination, and 2% incorrect identification, and 0% were unidentified. For clinical strains, there was 95.1% correct identification, 4.9% low discrimination, and 4.6% incorrect identification, and 0.3% were unidentified. The 4.6% (17/365) of clinical isolates that were incorrectly identified consisted of 14 isolates that were correct at the genus level and three that were incorrect at the genus level. The new ANC card met all performance criteria within a 95% confidence interval compared to the identification performance by 16S rRNA gene sequencing.

Evaluation of the New Vitek 2 ANC Card for Identification of Medically Relevant Anaerobic Bacteria

“…Indeed, for these latter, a correct identification rate of 91.7% was achieved after the application of additional tests. Overall, these results are comparable to those recently reported by other authors evaluating the Vitek 2 ANC system (11,15). As in those studies, difficulties were encountered in the present study in identifying clostridia species, except for C. perfringens.…”

Evaluation of the Vitek 2 ANC Card for Identification of Clinical Isolates of Anaerobic Bacteria

“…With our recommendations, the correct species-and genus-level identifications would increase from 60.1% (181/ 301) and 79.4% (239/301) to 70.1% (211/301) and 81.1% (244/ 301) of isolates, respectively. These percentages of correct identification are still lower than those reported previously (15,17). However, including the previously reported 169 excluded isolates (17), which were not included in the system, correct genus-and species-level identifications of 90.0% and 67.0% of isolates, respectively, would be obtained.…”

“…However, species and genera not present in the database had been eliminated from their study isolates (15,17). The lower level of correct identification obtained in our clinical study can be explained by the inclusion of test isolates that are not present in the database but are encountered in clinical material.…”

“…This is in contrast to the methods used in two previously reported studies (15,17). The identification obtained by use of the Vitek 2 ANC system was compared with that obtained by use of 16S rRNA gene sequencing.…”

“…In order to assess the accuracy of the ANC card in a "reallife" setting, unknown clinical isolates of anaerobic bacteria were used, regardless of whether the species are present in the Vitek database. This is in contrast to the methods used in two previously reported studies (15,17). The identification obtained by use of the Vitek 2 ANC system was compared with that obtained by use of 16S rRNA gene sequencing.…”