Do you treat with antibiotics active against methicillin-resistant staphylococci when a patient's culture grows non-lugdunensis, coagulase-negative staphylococci that tests susceptible to oxacillin by phenotypic testing, given the low constitutive PbP2A production of most CoNS?

Most coagulase-negative staphylococci (80%) are truly methicillin-resistance. All coagulase-negative Staphylococci, other than S. lugdunensis, have low constitutive or basal production of PbP2A in the absence of induction. As a result, phenotypic testing for oxacillin resistance is insensitive. Consequently, these Staph species, when isolated by culture, are considered oxacillin/methicillin resistant, even when phenotypic testing shows susceptibility. In other words, most coagulase-negative Staphylococci (except S. lugdunensis), are oxacillin/methicillin resistant, even when phenotypic testing shows susceptibility, Historically, it has been recommended to treat all coagulase-negative isolates with an antibiotic with activity against MRSA.