Methicillin-resistant Staphylococcus aureus: evaluation of detection techniques on laboratory-passaged organisms

Strains of methicillin-resistant Staphylococcus aureus (MRSA) are a major cause of nosocomial infection. This has led to the widespread introduction of screening techniques to identify patients or staff colonised with the organism and prevent the spread of MRSA in the hospital environment. The aim of laboratory techniques for the detection of MRSA screening is the rapid isolation and identification of MRSA, enabling timely implementation of appropriate infection control measures. This study compares commercially available products used by the majority of laboratories during routine screening of samples for MRSA. Several selective media are tested, including mannitol salt agar, Mueller Hinton agar, milk agar and blood agars. The accuracy of combining rapid agglutination from selective media for identification of MRSA is also determined, using six commercially produced kits. Owing to debate concerning the use of enrichment broth, in addition to primary isolation on solid media, four enrichment broths are tested and compared to direct culture techniques. Using a selection of laboratory-passaged MRSA phage types, results demonstrated that mannitol salt agar containing 75 g/L NaCl, without the addition of oxacillin, recovered all 50 MRSA strains and produced the highest isolation rate. Robertson's cooked-meat broth, with 7.5% NaCl, proved the most effective enrichment medium and was more sensitive than direct culture by 3%. Pastorex Staph-plus proved to be the most efficient rapid agglutination kit when testing MRSA colonies removed directly from selective agars.