Comparative evaluation of a rapid MRSA detection assay based on multiplex real-time PCR versus MRSA screening cultures containing egg yolk

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°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.