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Journal of Clinical Microbiology, September 2009, p. 2879-2882, Vol. 47, No. 9
0095-1137/09/$08.00+0     doi:10.1128/JCM.01109-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

BD Phoenix and Vitek 2 Detection of mecA-Mediated Resistance in Staphylococcus aureus with Cefoxitin{triangledown}

Alan D. Junkins, Shawn R. Lockhart, Kristopher P. Heilmann, Cassie L. Dohrn, Diana L. Von Stein, Patricia L. Winokur, Gary V. Doern, and Sandra S. Richter*

University of Iowa Carver College of Medicine, Iowa City, Iowa

Received 7 June 2009/ Returned for modification 8 July 2009/ Accepted 13 July 2009

The BD Phoenix (BD Diagnostics, Sparks, MD) and Vitek 2 (bioMérieux, Durham, NC) automated susceptibility testing systems have implemented the use of cefoxitin to enhance the detection of methicillin (meticillin)-resistant Staphylococcus aureus (MRSA). To assess the impact of this change, 620 clinically significant S. aureus isolates were tested in parallel on Phoenix PMIC/ID-102 panels and Vitek 2 AST-GP66 cards. The results for oxacillin and cefoxitin generated by the automated systems were compared to those generated by two reference methods: mecA gene detection and MICs of oxacillin previously determined by broth microdilution according to CLSI guidelines. Testing of isolates with discordant results was repeated to attain a majority or consensus final result. There was 100% final agreement between the results of the two reference methods. For the 448 MRSA and 172 methicillin-susceptible S. aureus isolates tested, the rates of categorical agreement of the results obtained with the automated systems with those obtained by the reference methods were 99.8% for the Phoenix panels and 99.7% for the Vitek 2 cards. A single very major error occurred on each instrument (0.2%) with different MRSA isolates. The only major error was attributed to the Vitek 2 system overcalling oxacillin resistance. In 16 instances (9 on the Phoenix system, 7 on the Vitek 2 system), an oxacillin MIC in the susceptible range was correctly changed to resistant by the expert system on the basis of the cefoxitin result. The inclusion of cefoxitin in the Phoenix and Vitek 2 panels has optimized the detection of MRSA by both systems.

* Corresponding author. Mailing address: Department of Pathology, C606 GH, University of Iowa Roy J. and Lucille A. Carver College of Medicine, 200 Hawkins Drive, Iowa City, IA 52242-1009. Phone: (319) 356-2990. Fax: (319) 356-4916. E-mail: sandra-richter{at}uiowa.edu

{triangledown} Published ahead of print on 22 July 2009.

Journal of Clinical Microbiology, September 2009, p. 2879-2882, Vol. 47, No. 9
0095-1137/09/$08.00+0     doi:10.1128/JCM.01109-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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