Antimicrobial Activity of Daptomycin Tested Against Gram-Positive Strains Collected in European Hospitals: Results from 7 Years of Resistance Surveillance (2003-2009)

Daptomycin is a cyclic lipopeptide approved by the European Medicines Agency (EMEA) for the treatment of complicated skin and soft tissue infections (cSSTI) and Staphylococcus aureus bacteremia and endocarditis. We evaluated the in vitro activity of daptomycin and comparators tested against clinical isolates from European hospitals over a 7-year period (2003-2009). A total of 36,769 consecutive isolates were collected in 34 medical centers located in 13 European countries, Turkey and Israel. The collection included S. aureus (18,352; 27.2% oxacillin-resistant [MRSA]); coagulase-negative staphylococci (CoNS; 6,874), Enterococcus spp. (7,241; 9.4% vancomycin-resistant), beta-hemolytic (3,009), viridans group streptococci (1,176), and Streptococcus bovis/gallolyticus (107). The organisms were isolated mainly from patients with bloodstream infection (56%) or cSSTI (23%). Daptomycin was very active against S. aureus and CoNS (MIC50/90, 0.25/0.5 mg/L for both organisms), and its activity was not adversely influenced by oxacillin resistance. All Enterococcus faecalis strains were susceptible to daptomycin (MIC50/90, 1/1 mg/L). Daptomycin (MIC50/90, 2/2 mg/L; 100.0% susceptible) and linezolid (MIC50/90, 1/2 mg/L; 99.7% susceptible) were the most active agents tested against vancomycin-resistant E. faecium. Vancomycin-resistant and -susceptible enterococcal strains were equally susceptible to daptomycin. Daptomycin was also active against beta-hemolytic streptococci (MIC50/90, 0.06/0.25 mg/L; 100.0% susceptible), viridans group streptococci (MIC50/90, 0.25/0.5 mg/L; 99.8% susceptible) and S. bovis (MIC50/90, 0.06/0.12 mg/L; 100.0% susceptible). In summary, daptomycin was very potent against this large collection (36,769) of Gram-positive organisms isolated in European hospitals, and its activity remained stable across the 7-year period evaluated (2003-2009), using reference methods and interpretive criteria. Decreases in daptomycin potency were not observed since EMEA approval and widespread clinical use, and emerging resistance to other compounds did not adversely influence daptomycin activity against contemporary Gram-positive species.