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Methicillin-Resistant Staphylococcus aureus (MRSA) Screen

  • Perhaps the most efficient means for detecting methicillin-resistant staphylococci in clinical laboratories is the use of the agar dilution screening test.
  • Illustrated in the image is a Mueller-Hinton agar plate containing 6 ug/mL of oxacillin, previously inoculated with a strain of Staphylococcus aureus. Oxacillin is used as a marker for methicillin resistance because it is more stable in the agar medium. Growth on this screening medium is presumptive for methicillin resistance.
  • Thus, in the presence of growth, as shown here, a follow-up minimum inhibitory concentration (MIC) test must be performed to determine the exact level of resistance.