JCM Accepts, published online ahead of print on 14 October 2009

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Google Scholar Articles by Wolk, D. M. Articles by Schifman, R. B. PubMed PubMed Citation Articles by Wolk, D. M. Articles by Schifman, R. B.

 Previous Article  |  Next Article 

J. Clin. Microbiol. doi:10.1128/JCM.00601-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

A Comparison of MRSASelect^TM Agar, CHROMagarMRSA^TM, and Xpert MRSA^TM for Detection of Methicillin Resistant Staphylococcus aureus (MRSA) from the Nares' Specimens: Diagnostic Accuracy for Surveillance Samples with Various Bacterial Densities

D. M. Wolk^*, J. L. Marx, L. Dominguez, D. Driscoll, and R. B. Schifman

Southern Arizona VA Health Care System, Tucson, AZ; The University of Arizona/BIO5 Institute, Tucson, AZ

^* To whom correspondence should be addressed. Email: dwolk{at}email.arizona.edu.

Rapid laboratory methods provide optimal support for active surveillance efforts to screen for methicillin-resistant Staphyococcus aureus (MRSA). Most laboratories struggle to determine the optimal use of resources, considering options to balance cost, speed and diagnostic accuracy. To assess the performance of common methods, the first comparison of MRSASelect^TM Agar (MS), CHROMagar^TM MRSA (CA), with and without broth enrichment followed by a 24 hr subculture to MS agar, was performed. Results were compared to the Xpert^TM MRSA Assay. For direct culture methods, agreement between MS and CA was 98.8%. At 18 hrs, direct MS identified 93% of all positive samples from direct culture and 84% of those identified by the Xpert MRSA. For trypticase soy broth-enriched MS culture (TSB-MS), incubated overnight then subcultured for an additional 24 hrs, agreement with Xpert MRSA was 96%. Agreement between direct MS and Xpert MRSA was 100% when semi-quantitative culture revealed bacterial density of 2+ or greater; however, discrepancies between culture and Xpert MRSA arose for MRSA bacterial densities of 1+ or less, indicating low density as a common cause of false negative culture results. Since 1+ or less was established as the most common MRSA carrier state, broth enrichment or PCR may be a critical for identification of all MRSA carriers who may be reservoirs for transmission. In this active surveillance convenience sample, use of broth enrichment followed by subculture to MS offered a low cost but sensitive method for MRSA screening, with performance similar to Xpert MRSA PCR.