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Title
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Evaluation of chromogenic media for detection of methicillin-resistant **Staphylococcus aureus**
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Author
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Abstract
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| Rapid laboratory diagnosis is critical for treating, managing, and preventing methicillin-resistant Staphylococcus aureus (MRSA) infections. We evaluated and compared the potential for MRSA detection of five chromogenic media - Brilliance (Oxoid), ChromID (bioMérieux), MRSASelect (Bio-Rad), CHROMagar (CHROMagar-Microbiology), and BBL-CHROMagar (BD Diagnostics). Media were tested on log serial dilutions (100-106 cfu) of pure isolates of MRSA (n=60), non-MRSA (n=27), and their defined mixtures simulating clinical samples (n=84). Further evaluations were done on pre-enriched nasal and groin screening swabs (n=213) from 165 hospitalized patients. Randomized samples were spiral-plated on each medium and independently scored by 5 investigators for characteristic colonies at 24 and 48 hours incubation. Confirmatory testing was done on upto 5 putative MRSA colonies recovered from each medium. Cumulative average sensitivity on isolates, mixtures and clinical samples was highest for Brilliance (97), and similar for the other four media (≥92%). Cumulative average specificity was highest for BBL-CHROMagar (99%), followed by MRSASelect (98%), CHROMagar (97%), ChromID (89%), and Brilliance (86%). All media detected MRSA at 10 and 1 cfu, although at these low loads, few MRSA harboring SCCmec III- or IV were misinterpreted as non-MRSA by investigators. False-positive results were mainly due to methicillin-resistant S. epidermidis. For an arbitrary MRSA prevalence of 5% and based on patient sample evaluations, positive predictive values for BBL-CHROMagar and CHROMagar ({approx}84%) were highest. Negative predictive values of all media were ≥92% for MRSA prevalence ranging from 5%30%. In conclusion, BBL-CHROMagar and CHROMagar gave best overall results for detection of MRSA, irrespective of the sample concentration, investigator, or incubation period. |
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Language
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English
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Source (journal)
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Journal of clinical microbiology. - Washington, D.C.
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Publication
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Washington, D.C.
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2010
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ISSN
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0095-1137
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Volume/pages
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48
:4
(2010)
, p. 1040-1046
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ISI
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000276153200004
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Full text (Publisher's DOI)
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Full text (open access)
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