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Multiplex PCR Assay for Typing of Staphylococcal Cassette Chromosome Mec Types I to V in Methicillin-resistant Staphylococcus aureus
Published on: September 5, 2013
Comparative evaluation of a rapid MRSA detection assay based on multiplex real-time PCR versus MRSA screening
Yuko Sumitani1, Yoshio Kobayashi
1Department of Clinical Laboratories, School of Medicine, Keio University, 35 Shinano-machi, Shinjuku-ku, Tokyo, 160-0016, Japan. umiyama@sc.itc.keio.ac.jp
Abstract:
Although the Centers for Disease Control and Prevention (CDC) has been recommending the performance of active surveillance culture (ASC) for the prevention of methicillin-resistant Staphylococcus aureus (MRSA) infections and their control since the guideline was issued in 2006, many variant types of MRSA with various characteristics have been found recently. As this change in MRSA characteristics makes it harder to screen MRSA only by cultures, it is expected that ASC will not be sufficient for the prevention of MRSA infections or MRSA infection control. We evaluated the comparative utility of the BD GeneOhm MRSA assay (a rapid MRSA detection test based on a multiplex real-time polymerase chain reaction [PCR] assay; Becton Dickinson, Fukushima, Japan) and MRSA screening cultures containing egg yolk. The results of the BD GeneOhm MRSA assay were as follows: all MRSA strains were positive, including one strain which became positive by retest; all methicillin-resistant S. epidermidis (MRSE) strains and methicillin-sensitive S. epidermidis (MSSE) strains were negative; 11 of 12 methicillin-sensitive S. aureus (MSSA) strains were negative, while 1 strain was positive; ATCC 33591 was positive, and ATCC 29213 was negative. The sensitivity and specificity of the BD GeneOhm MRSA assay were 100% and 97.4%, respectively. Nine egg yolk reaction-negative MRSA strains were found in 50 MRSA strains, and all MRSE, MSSA, and MSSE strains were denied as MRSA on Pourmedia MRSA II (Eiken Chemical, Tokyo, Japan) after 24-h or 48-h incubation at 35 degrees C. The sensitivity and specificity of Pourmedia MRSA II were 82% and 100%, respectively. Similar results were obtained with some other cultures containing egg yolk.
Insights
Active surveillance cultures (ASC) may be insufficient for detecting emerging methicillin-resistant Staphylococcus aureus (MRSA) variants. A rapid PCR-based assay demonstrated higher sensitivity and specificity than traditional egg yolk cultures for MRSA screening.
Area of Science:
- Clinical Microbiology
- Infectious Diseases
- Molecular Diagnostics
Background:
- Active surveillance culture (ASC) has been recommended by the CDC since 2006 for preventing and controlling methicillin-resistant Staphylococcus aureus (MRSA) infections.
- Recent identification of MRSA variants with altered characteristics challenges the efficacy of traditional culture-based screening methods.
- The sufficiency of ASC for MRSA infection prevention and control is increasingly questioned due to these evolving MRSA strains.
Purpose of the Study:
- To comparatively evaluate the diagnostic utility of the BD GeneOhm MRSA assay, a rapid real-time PCR test.
- To assess the effectiveness of MRSA screening cultures containing egg yolk.
- To determine the sensitivity and specificity of both methods in detecting MRSA.
Main Methods:
- The BD GeneOhm MRSA assay was used to test various strains, including MRSA, methicillin-resistant S. epidermidis (MRSE), methicillin-sensitive S. epidermidis (MSSE), and methicillin-sensitive S. aureus (MSSA).
- MRSA screening cultures utilizing egg yolk (Pourmedia MRSA II) were employed for comparison.
- Standard microbiological incubation conditions (35°C for 24-48 hours) were applied to the culture methods.
Main Results:
- The BD GeneOhm MRSA assay showed 100% sensitivity and 97.4% specificity, correctly identifying all MRSA strains (with one requiring retest) and most MSSA strains.
- Egg yolk-based cultures (Pourmedia MRSA II) exhibited 82% sensitivity and 100% specificity, failing to detect nine MRSA strains.
- MRSE, MSSE, and most MSSA strains were correctly identified as negative by the egg yolk cultures.
Conclusions:
- The BD GeneOhm MRSA assay, a PCR-based method, offers superior sensitivity and specificity compared to traditional egg yolk-containing cultures for MRSA detection.
- Rapid molecular assays like the BD GeneOhm MRSA assay are crucial for accurately screening MRSA, especially given the emergence of variant strains.
- Traditional ASC methods using egg yolk may be insufficient for comprehensive MRSA infection control due to limitations in detecting certain MRSA strains.
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