Daptomycin resistance and treatment failure following vancomycin for methicillin-resistant Staphylococcus aureus (MRSA) mitral valve acute bacterial endocarditis (ABE).

Acute bacterial endocarditis (ABE) is most commonly due to virulent pathogens, i.e., Staphylococcus aureus. S. aureus ABE may be due to methicillin-sensitive (MSSA) or methicillin-resistant (MRSA) strains and, optimally, ABE should be treated with bactericidal antibiotics. Traditionally, vancomycin has long been used to treat MRSA ABE, but it has been shown that vancomycin may increase the staphylococcal the thickness, resulting in permeability-mediated resistance. We present a case of a 72-year-old male with mitral valve MRSA ABE refractory to daptomycin therapy following initial therapy with vancomycin. We were not able to diminish the intensity of the patient's MRSA bacteremia from his mitral valve ABE, even with high-dose (12 mg/kg day) daptomycin, presumably because of permeability-mediated resistance due to antecedent vancomycin therapy.