Potential Impact of the VITEK 2 System and the Advanced Expert System on the Clinical Laboratory of a University-Based Hospital

Abstract

A study was designed to assess the impact of the VITEK 2 automated system and the Advanced Expert System (AES) on the clinical laboratory of a typical university-based hospital. A total of 259 consecutive, nonduplicate isolates of Enterobacteriaceae members, Pseudomonas aeruginosa, and Staphylococcus aureus were collected and tested by the VITEK 2 system for identification and antimicrobial susceptibility testing, and the results were analyzed by the AES. The results were also analyzed by a human expert and compared to the AES analyses. Among the 259 isolates included in this study, 245 (94.6%) were definitively identified by VITEK 2, requiring little input from laboratory staff. For 194 (74.9%) isolates, no inconsistencies between the identification of the strain and the antimicrobial susceptibility determined by VITEK 2 were detected by the AES. Thus, no input from laboratory staff was required for these strains. The AES suggested one or more corrections to results obtained with 65 strains to remove inconsistencies. The human expert thought that most of these corrections were appropriate and that some resulted from a failure of the VITEK 2 system to detect certain forms of resistance. Antimicrobial phenotypes assigned to the strains by the AES for ␤-lactams, aminoglycosides, quinolones, macrolides, tetracyclines, and glycopeptides were similar to those assigned by the human expert for 95.7 to 100% of strains. These results indicate that the VITEK 2 system and AES can provide accurate information in tests for most of the clinical isolates examined and remove the need for human analysis of results for many. Certain problems were identified in the study that should be remediable with further work on the software supporting the AES.The VITEK 2 system is a new system that automatically performs rapid identification and antimicrobial susceptibility testing on a manually prepared inoculum (1). The Advanced Expert System (AES) is designed to analyze results generated by the VITEK 2 system for biologic validity and then provide comments on the results. One important function of the AES is to look for inconsistencies between the identification of the organism and the antimicrobial susceptibility of the isolate. Another important function is to ascertain the antimicrobial phenotype of the isolate based on results of susceptibility tests. A third function is to deduce the susceptibility of the organism to drugs not tested based on its susceptibility to the antibiotics actually tested.In a previous study, the ability of the AES to correctly ascertain the ␤-lactam phenotype of isolates of Enterobacteriaceae and Pseudomonas aeruginosa was determined using a panel of 196 strains collected worldwide which had been characterized by biochemical and molecular techniques for their ␤-lactamase content (6). The results of that study showed that the AES correctly identified the ␤-lactam phenotype of 183 (93.4%) of these isolates despite the inclusion of many rare phenotypes in the isolate panel. The study, however, did not assess the...

Characterization of Klebsiella isolates by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and determination of antimicrobial resistance with VITEK 2 advanced expert system (AES)

“…Canton et al (25) found the VITEK 2 method less reliable than the microdiffusion method, whereas Leclercq et al (26) stated that VITEK 2 was more reliable than the agar dilution method. According to Nyberg et al (27), sensitivity and specificity vary in different studies, but high sensitivity and specificity have been achieved with VITEK 2 when testing K. pneumoniae isolates (15,27,28). They also claimed that VITEK 2 AES was excellent compared to genotypic ESBL determination and it was very comparable to the agar dilution and diffusion methods.…”

“…The VITEK 2 advanced expert system (AES) is an automated system that uses antimicrobial susceptibility data to suggest the phenotype of the tested isolate and thereby determine its susceptibility or resistance to antibiotics (15).…”

Comparison of Phoenix and VITEK 2 Extended-Spectrum-β-Lactamase Detection Tests for Analysis of Escherichia coli and Klebsiella Isolates with Well-Characterized β-Lactamases

“…Ideally, an automated system that utilizes an ESBL confirmatory test and an expert system should accurately discriminate ESBLs from other ␤-lactamases and provide interpretations and recommendations that do not require additional input by laboratory personnel (10). Inconclusive or incorrect comments are likely to frustrate and cause confusion and may delay or even prevent the issue of a clinically useful report to the clinician.…”

Identification and Susceptibility Testing of Enterobacteriaceae and Pseudomonas aeruginosa by Direct Inoculation from Positive BACTEC Blood Culture Bottles into Vitek 2

“…The AES may also suggest a change in an interpretation from sensitive (S) to intermediate (I) or resistant (R), based on recognized resistance mechanisms, to prevent therapeutic failure. These changes of interpretation are according to the software parameters defined by the user (19). For the tests in the present study, interpretations as recommended by the National Committee for Clinical Laboratory Standards (15) and the AES configuration parameters set "natural resistance," "European hospitals," "never more susceptible," and "least risk" were used.…”