Isolation of methicillin-resistant Staphylococcus aureus from non-sterile sites: evaluation of a new selective medium

Methicillin-resistant Staphylococcus aureus (MRSA) are relatively common nosocomial isolates, causing problems for health-care professionals worldwide. Therefore, early detection of the organisms by the laboratory is essential. A new selective medium for MRSA is described, comprising a DNA-containing base and a combination of stains that permit direct visualisation of DNase activity around colonies. The medium is made partially selective by adding a number of antibiotics (aztreonam, polymyxin B, nystatin and oxacillin). When compared to other media used for the isolation of MRSA, it was found that the new medium allowed earlier detection of colonies and provided a good direct method of identification, reducing the need for time-consuming replating of colonies, and, therefore, the turnaround time for specimens entering the laboratory for MRSA screening.