Six cases of daptomycin-non-susceptible Staphylococcus aureus bacteraemia in Singapore

We report what we believe to be the first six cases of daptomycin-non-susceptible Staphylococcus aureus infections from Singapore. These strains were rapidly isolated after bacteraemic patients were switched to daptomycin following initial prolonged unsuccessful therapy with vancomycin, despite confirmation of daptomycin susceptibility just prior to initiating daptomycin therapy. The majority of post-vancomycin therapy strains exhibited marked thickening of their cell walls on electron microscopic examination. In patients with persistent S. aureus bacteraemia, therapeutic failure with daptomycin may occur if used as salvage therapy following vancomycin failure, notwithstanding initial susceptibility testing results.