Antimicrobial susceptibility of Gram-positive bacteria isolated from US medical centers: results of the Daptomycin Surveillance Program (2007–2008)

Gram-positive bacterial strains (12 443) consecutively collected during 2007 to 2008 in hospitals located in the United States were tested by reference broth microdilution methods against daptomycin and comparison agents. Methicillin (oxacillin) resistance rates were 55.9% and 74.0% for Staphylococcus aureus and coagulase-negative staphylococci, respectively, and the vancomycin resistance rate among Enterococcus faecalis and Enterococcus faecium were 5.4% and 75.4%, respectively. Daptomycin was very active against all Gram-positive species with MIC90 values of 0.5, 0.25, 0.5, and 2 μg/mL for staphylococci, β-hemolytic streptococci, viridans group streptococci, and enterococci, respectively. Overall, 99.9% of S. aureus, 100.0% of E. faecalis, and 99.5% of E. faecium were susceptible to daptomycin. In addition, daptomycin MIC distributions for S. aureus and enterococci from 2007 to 2008 were very similar to those from 2002 to 2003. In summary, high rates of methicillin-resistant staphylococci and vancomycin-resistant enterococci were observed in US hospitals, but daptomycin remains active against these clinically important Gram-positive organisms with no evidence of potency loss since its approval for clinical use in late 2003.