ABSTRACT
There is an increasing need for alternative agents in endocarditis, especially with the increasing incidence of vancomycin-intermediate Staphylococcus aureus (VISA). We evaluated the in vitro activity of daptomycin and several comparator agents against 33 non-duplicate clinical Staphylococcus aureus isolates from intravenous drug users with right endocarditis. Wider microdilution panels were used for all the comparator agents and daptomycin. Daptomycin was also tested using E-test strips. E-test strips were used to confirm the vancomycin MICs. Methicillin-resistant Staphylococcus aureus (MRSA isolates with vancomycin MICs ≥ 2 g/mL were screened using the E-test GRD. In all, 30 isolates were methicillin-susceptible (MSSA) and 3 MRSA. The three MRSA isolates exhibited a false vancomycin MIC >2 g/mL determined by Wider microdilution panels. They were screened using the E-test GRD and they were GRD negative. Their final MIC was 2 g/mL. Three MSSA and three MRSA isolates had a vancomycin MIC of 2 g/mL. Four MSSA isolates had a vancomycin MIC of 1.5 g/mL, daptomycin MIC90 0.25 g/mL, linezolid MIC90 2 g/mL. As regards daptomycin, wider microdilution panels and E-test strips yielded the same results. Our findings suggest that daptomycin and linezolid are a viable alternative for treating right endocarditis and bacteraemia caused by MSSA, MRSA and hVISA.
