Methicillin-Resistant Staphylococcus aureus (MRSA) Disk Test
- The disk diffusion test can also be used in the detection of methicillin-resistant Staphylococcus aureus (MRSA).
- Illustrated in the image is the surface of a Mueller-Hinton agar plate previously inoculated with a strain of S. aureus suspected of being methicillin-resistant. Although the zone of inhibition is at the borderline for resistance (18 mm); the presence of small colonies within the zone of inhibition (yellow arrows) indicates the presence of heteroresistant strains.
- The interpretation here, therefore, is "methicillin-resistant" staphylococci, even though the zone diameter appears to be adequate. The detection of the heteroresistant strains indicates that minimum inhibitory concentration (MIC) studies are required.