in a Clinical Endocarditis Isolate of Staphylococcus aureus

Using isogenic clinical bloodstream Staphylococcus aureus strains from a patient with relapsing endocarditis, we in-vestigated the transcriptional profiles of the mprF and dlt genes in the context of cell-surface charge and daptomycin nonsusceptibility. As in prior studies, a point mutation within mprF was observed in the daptomycin-nonsusceptible strain. However, neither the transcriptional profile of mprF nor the membrane phospholipid analyses were compatible with the anticipated mprF gain-in-function phenotype. In contrast, we demonstrated enhanced dlt expression coinci-dent with increased positive surface charge and reduced dap-tomycin binding. With the increasing use of daptomycin in clinical practice, there have been a number of recent reports of strains of Staphylo-coccus aureus (especially methicillin-resistant S. aureus) devel-oping daptomycin nonsusceptibility during therapy with this agent [1, 2]. Some, but not all, of these daptomycin-nonsus-ceptible clinical strains exhibit distinct single-nucleotide poly-morphisms (SNPs) within the mprF gene, in association wit