A rapid (20 h) solid screening medium for detecting methicillin-resistant Staphylococcus aureus

Methicillin aztreonam mannitol salt agar is a sensitive and reliable solid screening medium for detecting methicillin-resistant Staphylococcus aureus (MRSA). With this medium an incubation period of only 20 h is sufficient to either produce visible colonies of MRSA or to exclude MRSA (no staphylococcal colonies). Coagulase testing (requiring a further 6 h) enables coagulase-positive isolates to be provisionally reported as ‘possible MRSA’ 26–30 h after the swabs were collected. The medium supports growth of intrinsically resistant staphylococci including low-expression-class MRSA (methicillin minimum inhibitory concentration (MIC) 8–16mg/L), but methicillin susceptible staphylococci and β-lactamase hyperproducers are suppressed.