gram-negative bacilli. AutoMicrobic system for

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Comparison of the autoSCAN-W/A rapid bacterial identification system and the Vitek AutoMicrobic system for identification of gram-negative bacilli. M A Pfaller, D Sahm, C O'Hara, C Ciaglia, M Yu, N Yamane, G Scharnweber and D Rhoden J. Clin. Microbiol. 1991, 29(7):1422.

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Vol. 29, No. 7

JOURNAL OF CLINICAL MICROBIOLOGY, JUlY 1991, P. 1422-1428

0095-1137/91/071422-07$02.00/0 Copyright © 1991, American Society for Microbiology

Comparison of the AutoSCAN-W/A Rapid Bacterial Identification System and the Vitek AutoMicrobic System for Identification of Gram-Negative Bacilli M. A. PFALLER, 12t* D. SAHM,3 C. O'HARA,4 C. CIAGLIA,3 M. YU,2 N. YAMANE,2 G. SCHARNWEBER,l AND D. RHODEN4 Iowa City Veteran's Affairs Medical Center' and University of Iowa College of Medicine,2 Iowa City, Iowa 52242; University of Chicago, Chicago, Illinois 606373; and Centers for Disease Control, Atlanta, Georgia 303334 Received 27 December 1990/Accepted 22 April 1991

based instrumentation which can incubate, read, and interpret the enzymatic tests, thus providing greater standardization, accuracy, and reproducibility and less hands-on time than more conventional identification systems (3, 5, 6, 8, 11, 16, 26). Although there are a number of instrument-assisted approaches available for bacterial identification (3, 6, 8, 11, 16-18, 20-26), these systems usually require several manual steps and cannot be considered truly automated. The recently introduced autoSCAN-W/A (W/A) with the rapid fluorometric gram-negative identification panel (Rapid Neg Combo 1 [RNC] panel; Baxter MicroScan, West Sacramento, Calif.) provides a fully automated approach to the identification of gram-negative bacilli which utilizes fluorogenic substrates and a 2-h incubation time. The W/A, the Vitek AutoMicrobic System (Vitek AMS; Vitek Systems, Inc., Hazelwood, Mo.), and the API ALADIN (Analytab Products, Plainview, N.Y.) are the only truly automated microbiology systems available (3, 6, 17, 18, 22-26). Although studies comparing the W/A with more conventional manual and instrument-assisted identification systems are necessary (19, 26), it is equally important to compare the W/A rapid identification system with other fully automated test systems, such as the Vitek AMS. We performed a collaborative study to evaluate the performance of the W/A rapid fluorometric identification system versus that of the Vitek AMS for identification of gram-negative bacilli. The study consisted of two phases. Phase I was a clinical challenge in which recent isolates obtained at the two participating medical centers were tested on both systems in the respective laboratories. In phase II, a common set of 134 isolates of gram-negative bacilli was tested in both laboratories as a means of determining interlaboratory agreement using both the W/A and the Vitek AMS.

Diagnosis and therapy of gram-negative bacterial infection in hospitalized patients remains a major challenge for clinical microbiology laboratories. The continued prominence of gram-negative bacilli as major pathogens in intensive care unit patients (14), development of limited-spectrum antibiotics and antibiotic-resistant bacteria, and the need to define the epidemiology of nosocomial infections all require that laboratories provide rapid, accurate, and cost-effective identification of clinical isolates of gram-negative bacilli (5, 15, 18, 21). Although the classical macrotube methods of bacterial identification remain useful as reference methods, they are too slow, cumbersome, and subjective for routine use in a clinical microbiology laboratory. The state of the art is the systems approach to identification, with emphasis on speed, standardization, reproducibility, and recently mechanization and automation (1-3, 5, 6, 8, 9, 11, 16-18, 20-26). Thus, the classical methods of identification have been adapted to miniaturized test systems which employ numerical coding, computerized data bases, and reaction endpoints which can be reached after 2 to 6 h of incubation (1-3, 5, 6, 8, 9, 11, 16-18, 20-26). One of the more recent advances in the rapid identification of pathogenic microorganisms is the use of chromogenic or fluorogenic substrates to assess preformed enzyme activity. By detecting preformed enzymes, these systems provide a rapid means of identifying clinically important organisms within 2 to 4 h of inoculation (23, 26). In addition, these identification systems can be coupled with microprocessorCorresponding author. t Present address: Department of Pathology, Oregon Health Sciences University, 3181 S.W. Sam Jackson Park Road, Portland, OR 97201. *

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The autoSCAN-W/A (W/A; Baxter MicroScan, West Sacramento, Calif.) with the new fluorometric Rapid Neg Combo 1 (RNC) panel is a fully automated fluorometric system for identification of both enteric and nonenteric gram-negative bacilli within 2 h. We compared the W/A with the Vitek AutoMicrobic System (Vitek AMS; Vitek Systems, Inc., Hazelwood, Mo.) for identification of 383 clinical isolates of gram-negative bacilli. The API 20E (Analytab Products, Plainview, N.Y.) and conventional biochemical testing were used as the reference systems. The W/A correctly identified 336 isolates (87.7%) to the species level and classified an additional 29 isolates (7.6%) as correct with low probability (overall identification = 95.3%); the Vitek AMS correctly identified 355 isolates (92.7%) to the species level and classified an additional 8 isolates (2.1%) as correct with low probability (overall identification = 94.8%). A common set of 134 isolates of gram-negative bacilli was tested in both participating laboratories as a means of assessing interlaboratory agreement with both the W/A and the Vitek AMS. The overall agreements between the two laboratories were 86% with the W/A and 92% with the Vitek AMS. The W/A performed comparably to the Vitek AMS for identification of most gram-negative bacilli, actually exceeding the Vitek AMS for identification of nonenteric bacilli. Rapid time to identification and a high level of automation make the W/A an attractive system for clinical microbiology laboratories.

VOL. 29, 1991

(This work was previously presented in part [24].)

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ware were used as recommended by the manufacturer. The disposable 30-well gram-negative identification card consisted of 29 lyophilized biochemicals and a growth control well. The inoculum was prepared in 1.8 ml of sterile saline, and the turbidity was adjusted to match that of a 1.0 McFarland standard. The card was inoculated by using the evacuator-sealer module, and the results of a manual oxidase test were entered by marking the card as directed by the manufacturer. The card was then placed into the 35°C reader-incubator module and automatically read once per hour by the optical scanner, which determined colorimetric and turbidimetric changes and compared each reading with the initial base reading. The percent change for each well was calculated to determine a positive or negative reaction. Final results were available in 4 to 13 h for isolates of the family Enterobacteriaceae and in 6 to 18 h for nonenteric gram-negative organisms. The results of each biochemical test were printed out along with a biotype number and the percent likelihood of identification for the organism being tested. The identifications were compared with those obtained by the reference system (API 20E plus conventional biochemical tests) and were classified as (i) correct to species, in which the first-choice identification had an excellent identification likelihood of equal to or greater than 90% as determined by the manufacturer's computer data base and was correct; (ii) correct with low probability (CLP), in which the correct identification was listed within a spectrum of choices, all of which had a likelihood of