Staphylococcal Endocarditis on Native Valves or Prosthetic Material Native Valve IE Staphylococci may be coagulase positive (S aureus) or coagu- lase negative (S epidermidis and various other species) and appear to have overtaken streptococci as the most common cause of IE in children in recent years.24,110,111 This may be attributable in part to the proliferation of intravascular cath- eters, as well as the nonspecificity of the Duke criteria in children causing false-positive diagnoses.Almost all staphylo- cocci are highly resistant to penicillin G and ampicillin.125 For those few that are susceptible to penicillin, penicillin or ampi- cillin will be effective, assuming a highly qualified laboratory has performed antibiotic susceptibility tests. Staphylococci that are susceptible to -lactamase resistant penicillins are termed methicillin susceptible or MSSA and may be S aureus or coagulase-negative strains such as S lugdunensis, which is typically susceptible and acts similarly to S aureus. In some centers, S aureus resistant to -lactamase resistant penicil- lins are termed MRSA, or ORSA or NRSA to indicate that oxacillin and nafcillin are the available penicillinase-resistant Baltimore et al Infective Endocarditis in Childhood: 2015 Update 1503 penicillins and methicillin is no longer available. The usually accepted current standard of care for methicillin-susceptible S aureus endocarditis involving a native valve or other native cardiac tissue includes a semisynthetic, -lactamase resistant penicillin (nafcillin or oxacillin) given intravenously for a minimum of 4 to 6 weeks, assuming there has been an appro- priate microbiological and clinical response to therapy. The addition of gentamicin for the first 3 to 5 days is an option and may accelerate the killing of the staphylococci, but this concept is based on extrapolation from experimental models. 