Difficult-To-Detect Staphylococcus aureus: mecA -Positive Isolates Associated with Oxacillin and Cefoxitin False-Susceptible Results

Abstract

In August of 2018, the United States Food and Drug Administration (FDA) announced a class I recall associated with a methicillin-resistant Staphylococcus aureus (MRSA) safety alert. This was due to failure to identify certain isolates as MRSA when using Gram-positive antimicrobial susceptibility testing (AST) cards with the Vitek 2 automated testing instrument (ATI) (1). To assist with the investigation, the U.S. Centers for Disease Control and Prevention (CDC) obtained 30 isolates identified during the initial recall from the National Reference Center for Staphylococci, Lyon, France. These isolates, reported as PCR-positive for mecA, produced susceptible results for oxacillin and cefoxitin (a surrogate for oxacillin) using AST cards on an ATI. Here, we describe the characterization of these isolates and announce their availability in the CDC and FDA Antibiotic Resistance Isolate Bank (AR Isolate Bank; https://wwwn.cdc.gov/ARIsolateBank/).