Distinct Subpopulations of Intravalvular Methicillin-Resistant Staphylococcus aureus with Variable Susceptibility to Daptomycin in Tricuspid Valve Endocarditis

Abstract

We present a case of endocarditis wherein organisms cultured from different valve leaflets yielded different daptomycin susceptibilities from each other and from organisms obtained from peripheral blood culture. Genomic analyses showed mutations in <i>mprF, purR</i>, and <i>agrA</i> Pharmacokinetic simulations showed consistent activity of daptomycin plus beta-lactam against all subpopulations. This represents an opportunity to understand <i>S. aureus</i> evolution and fitness <i>in vivo</i> on daptomycin therapy and the role of beta-lactams to prevent the selection of daptomycin-resistant subpopulations.