The prevalence of Methicillin-resistant Staphylococcus aureus (MRSA) has steadily increased over the past 40 years. Today, intravenous clindamycin or vancomycin is recommended for anti-staphylococcal coverage. Failure to identify resistant strains could result in the overuse of vancomycin and subsequent resistance to that antibiotic. Concerns over the emergence of this pathogen has caused many hospital laboratories to reassess their ability to identify antibiogram patterns and epidemiological shifts, determine appropriate laboratory testing, and review empiric therapy guidelines. Reliance on automated instrumentation to detect these isolates can result in major errors that cause false susceptible interpretations. The emergence of methicillin/oxacillin resistant strains has required additional laboratory analysis. This paper will review these tests and will focus on the role of the “D-test” in directing antibiotic therapy.

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