Comparative evaluation of the VITEK 2 Advanced Expert System (AES) in five UK hospitals

• Published in: Journal of antimicrobial chemotherapy Vol. 51; no. 5; pp. 1191 - 1202
• Main Authors: Barry, J., Brown, A., Ensor, V., Lakhani, U., Petts, D., Warren, C., Winstanley, T.
• Format: Journal Article
• Language: English
• Published: Oxford Oxford University Press 01.05.2003; Oxford Publishing Limited (England)
• Subjects: automated AST; Bacteria - drug effects; Bacteriological methods and techniques used in bacteriology; Bacteriology; Biological and medical sciences; Drug Resistance, Bacterial; Enterococcus; Enterococcus - drug effects; Expert; Expert Systems; Fundamental and applied biological sciences. Psychology; Gram-Negative Bacteria - drug effects; Microbial Sensitivity Tests - instrumentation; Microbiology; Phenotype; Staphylococcus; United Kingdom; VITEK 2; British Isles; Resistance; Phenotype; Sensitivity resistance; Automaton; Drug susceptibility test; Expert system
• ISSN: 0305-7453; 1460-2091; 1460-2091
• DOI: 10.1093/jac/dkg234

Objectives: We carried out an evaluation of VITEK 2 in five UK laboratories, comparing results with ‘gold standard’ agar-dilution MIC data, assessing its ability to recognize resistant phenotypes and comparing results with those generated by routine antimicrobial susceptibility testing methods. Methods: Laboratories tested a collection of 82 strains selected on the basis of their challenging and characterized resistance mechanisms. Results: In comparison with the reference MIC method, VITEK 2 gave an essential agreement of 304/315 (enterococci), 1619/1674 (staphylococci) and 2937/3074 (Gram-negative bacilli): overall 96.0% agreement. Corresponding category (SIR) agreements with VITEK 2 were 247/252, 1496/1561 and 2478/2626 (overall 95.1%). Using five routine methodologies, category agreements ranged from 58/63 to 45/45; 222/232 to 174/174, and 333/372 to 250/259 for the three organism groups with an overall agreement of 95.0%. In contrast to VITEK 2 Advanced Expert System (AES), routine microbiology laboratories did not attempt to detect resistance mechanisms for every antibiotic studied. VITEK 2 AES detected all 19 resistance mechanisms in enterococci: where applicable, routine methods detected 14, 10 and 10. Of 30 resistance mechanisms in staphylococci, VITEK 2 AES detected 25 compared with 23, 20, 17 and 18 detected by routine methods. Finally, of 44 resistance mechanisms in Gram-negative bacilli, VITEK 2 AES detected 30 compared with 30, 23, 15 and 10 detected by routine methods. Conclusions: VITEK 2 performed susceptibility tests accurately and the AES detected and interpreted resistance mechanisms appropriately. Heavy inocula in a liquid medium possibly favour better expression of certain resistance determinants. Although certain routine microbiology methods performed adequately, VITEK 2 AES offers a rapid, standardized method suited to laboratories lacking experience of resistance mechanisms and/or those not testing an appropriate number, or range, of antibiotics to detect resistance phenotypes.