Daptomycin nonsusceptibility in Staphylococcus aureus with reduced vancomycin susceptibility is independent of alterations in MprF

A previous study documented the presence of mutations in mprF that accompanied the loss of daptomycin susceptibility among Staphylococcus aureus isolates following exposure to the drug. An association between the development of glycopeptide-intermediate S. aureus and daptomycin nonsusceptibility has also been recently described. We report that among three clinical S. aureus isolates which developed vancomycin heteroresistance, as well as daptomycin nonsusceptibility despite a lack of exposure to this drug, there were no mutations resulting in amino acid substitutions in MprF.