JCM Accepts, published online ahead of print on 4 November 2009

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J. Clin. Microbiol. doi:10.1128/JCM.01555-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Spectra^TM MRSA, A New Chromogenic Agar Medium to Screen for Methicillin-Resistant Staphylococcus aureus

Jess F. Peterson, Katherine M. Riebe, Gerri S. Hall, Deborah Wilson, Susan Whittier, Elizabeth Palavecino, and Nathan A. Ledeboer^*

Dynacare Laboratories, Milwaukee, WI; Department of Pathology, Medical College of Wisconsin, Milwaukee, WI; Clinical Microbiology, Cleveland Clinic Foundation, Cleveland, OH; Clinical Microbiology Service, Columbia University Medical Center, New York, NY; Clinical Microbiology, Wake Forest University Baptist Medical Center, Winston-Salem, NC

^* To whom correspondence should be addressed. Email: nledeboe{at}mcw.edu.

A novel chromogenic media, Spectra^TM MRSA (Remel, Lenexa, KS), was designed to detect methicillin-resistant Staphylococcus aureus (MRSA) rapidly and more efficiently than traditional media (i.e., SBA, MSA). A multi-center study (including four clinical trial sites), and the Medical College of Wisconsin (MCW; Milwaukee, WI), compared the performance of Spectra^TM MRSA to traditional media in detecting MRSA. For this study, 767 nasal specimens from the multi-center study (traditional media used: SBA), and 667 nasal specimens from MCW (traditional media used: MSA), were plated on each test medium and examined after 24 and 48 h of incubation. At 24 h, the sensitivity and specificity of each medium were as follows: multi-center study: Spectra^TM MRSA, 95.4%, 99.7%; SBA, 93.6%, 100%; MCW: Spectra^TM MRSA, 95.2%, 99.5%; MSA, 88.7%, 94.0%. The positive predictive values (PPV) of each medium at 24 h were as follows: Multi-center study: Spectra^TM MRSA, 98.1%; SBA, 100%; MCW: Spectra^TM MRSA, 95.2%; MSA, 60.4%. In our evaluation, we found that Spectra^TM MRSA was able to rapidly identify and differentiate methicillin-resistant S. aureus from methicillin-susceptible S. aureus based on the utilization of chromogens that result in denim blue colonies, thus eliminating the need for biochemical analysis and antimicrobial susceptibility testing. Extending the incubation beyond 24 h did not significantly improve the recovery of MRSA and resulted in decreased specificity.