Post Traumatic Wound Infection: Testing for Methicillin Resistance

MRSA Disk Test

  • The disk diffusion test can also be used in the detection of methicillin-resistant Staphylococcus aureus.
  • Illustrated in the photograph 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 MIC studies are required.

Earn ASCLS P.A.C.E.® credits for your AMT, ASCP, or NCA recertification requirements.

Current Topics in Clinical Microbiology course details »

Learn more about medical technologist continuing education for MTs, MLTs, and other lab personnel »

Get information on laboratory compliance training for clinical and medical laboratories »