Critical evaluation of the AutoMicrobic system gram-negative identification card for identification of glucose-nonfermenting gram-negative rods

Abstract

During a 6-month study we critically evaluated the accuracy of the AutoMicrobic system Gram-Negative Identification Card (Vitek Systems, Inc., Hazelwood, Mo.) in identifying glucose-nonfermenting gram-negative bacilli by testing 419 selected isolates in parallel with a conventional reference method. Of 356 isolates included in the AutoMicrobic system profile, a total of 307 (86.2%) were correctly identified, 36 (10.1%) were not identified, and 13 (3.7%) were misidentified. Fifty-eight of 63 (92%) isolates not included in the profile were correctly reported as "unidentified organisms." Overall, if the first-choice identification was always accepted, only 18 (4.3%) isolates would have been incorrectly reported. When first-choice identifications appended with the special message "questionable biopattern" were rejected, and organisms were screened for characteristic odor and antimicrobial susceptibility before final acceptance of the AutoMicrobic system report, the number of misidentifications was reduced to 5 (1.2%). The average time to identification with the AutoMicrobic system Gram-Negative Identification Card was 15 h. This compares favorably with the 65 h required by the reference method.

Accuracy of four commercial systems for identification of Burkholderia cepacia and other gram-negative nonfermenting bacilli recovered from patients with cystic fibrosis

“…Published evaluations exist for each of the four commercial systems evaluated in the present study (1,2,4,11,14,15,17,22,23). However, only one of those studies, the one by Kitch et al (11), specifically states if any of their study isolates were recovered from CF patients.…”

“…Instead of not giving an identification for this organism, the system assigned an incorrect identification to eight of nine B. gladioli isolates, including five as B. cepacia. The Vitek card has been evaluated in several laboratories (14,15,17,22). However, only two studies have evaluated the system with multiple isolates of B. cepacia and related organisms.…”

“…Other organisms including P. aeruginosa, Pseudomonas putida, and Stenotrophomonas maltophilia were misidentified as B. cepacia. In the second evaluation (15), 27 of 32 B. cepacia isolates were correctly identified. The problem of misidentification appears to have been addressed in the database since no isolates were misidentified in the study (15).…”

“…In the second evaluation (15), 27 of 32 B. cepacia isolates were correctly identified. The problem of misidentification appears to have been addressed in the database since no isolates were misidentified in the study (15). In our study, 29 of 58 B. cepacia strains were accurately identified by the Vitek system.…”

Automated systems for identification of microorganisms.

“…Plorde et al (96) evaluated the GNI for identification of 419 non-glucose-fermenting gram-negative bacilli representing 14 genera and 35 species. The isolates were identified by conventional biochemicals.…”