JAC Advance Access published online on April 14, 2003
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkg234
© 2003 by The British Society for Antimicrobial Chemotherapy
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Original article
1 Department of Microbiology,
University Hospital, Birmingham
* Corresponding author. E-mail: tgwinstanley{at}hotmail.com.
Received 3 January 2003
; revised 18 February 2003
; accepted 26 February 2003
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.
Keywords: VITEK 2; Expert; automated AST
Comparative evaluation of the VITEK 2 Advanced
Expert System (AES) in five UK hospitals
2 Department
of Microbiology,
Ninewells Hospital, Dundee
3 Department
of Infection, Guy's & St Thomas' Hospital,
London
4 Department of Microbiology,
Basildon Hospital, Basildon, Essex
5 Department of Microbiology,
Royal Hallamshire Hospital, Glossop Road, Sheffield, UK
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