Comparison of four methods for detection of teicoplanin resistance in methicillin-resistant Staphylococcus aureus

To determine which method of determining the MIC of teicoplanin produces a result closely related to outcome in the critically ill patient.

Four methods of teicoplanin susceptibility testing-disc diffusion, Etest, VITEK (Legacy and VITEK 2) and agar incorporation-were compared for 47 methicillin-resistant Staphylococcus aureus (MRSA) isolates from invasive intensive care unit (ICU) infections and 83 isolates from ICU patients colonized with the organism. Clinical outcome was recorded prospectively for all the patients. Another 13 reference laboratory strains of MRSA with reduced susceptibility to teicoplanin were tested.

Both VITEK systems failed to demonstrate resistance in the three isolates identified as resistant by Etest or agar incorporation, and disc testing detected only one resistant isolate. A higher MIC, as found by Etest or agar incorporation, was associated with lower survival (n = 130, 95% CI -0.082 to -0.006, P = 0.023, Etest; n = 130, 95% CI -0.156 to -0.020, P = 0.011, agar). The findings for the 13 reference strains were similar, with a > or = 4-fold reduction in MIC between agar incorporation or Etest and VITEK2 for six isolates.

Neither disc diffusion nor the VITEK systems are reliable for detection of teicoplanin resistance in MRSA. Etest and agar incorporation remain the methods of choice.