Bactericidal activity of daptomycin versus vancomycin in the presence of human albumin against vancomycin-susceptible but tolerant meticillin-resistant (MRSA) with daptomycin minimum inhibitory concentrations of 1–2μg/mL

M. Torrico (1) , M.J. Giménez (1) , N. González (1) , L. Alou (1) , D. Sevillano (1) , F. Cafini (1) , J. Prieto (1) , R. Cleeland , L. Aguilar (1)

1 Microbiology Department

This study explored the influence of vancomycin tolerance and protein binding on the bactericidal activity of vancomycin versus daptomycin (protein binding 36.9% vs. 91.7%, respectively) against four vancomycin-tolerant meticillin-resistant (MRSA) [minimum inhibitory concentration/minimum bactericidal concentration (MIC/MBC)=0.5/16, 1/32, 2/32 and 1/32μg/mL for vancomycin and 1/1, 1/2, 2/2 and 2/4μg/mL for daptomycin]. Killing curves were performed with vancomycin/daptomycin concentrations equal to serum peak concentrations () (65.70/98.60μg/mL) and trough concentrations ) (7.90/9.13μg/mL) in the presence and absence of a physiological human albumin concentration (4g/dL), controlled with curves with the theoretical free drug fraction of vancomycin/daptomycin (41.45/8.18μg/mL) and (4.98/0.76μg/mL). Vancomycin and concentrations, regardless of the media, showed a bacteriostatic profile not reaching a reduction of 99% or 99.9% of the initial inocula during the 24-h experimental time period. Daptomycin antibacterial profiles significantly differed when testing and . was rapidly bactericidal (≤4h) with>5 log reduction in the initial inocula for all strains, regardless of the presence or not of albumin or the use of concentrations similar to free . exhibited similar final colony counts at 0h and 24h in curves with albumin, but with >3 log colony-forming units (CFU)/mL reduction at ≤4h for strains with an MIC of 1μg/mL and ca. 2 log CFU/mL reduction at ≤6h for strains with an MIC of 2μg/mL. This activity was significantly higher than the activity of the free fraction. The results of this study reinforce the idea that pharmacodynamics using concentrations calculated using reported protein binding are unreliable. Daptomycin exhibited rapid antibacterial activity against vancomycin-tolerant MRSA isolates even against those with high daptomycin MICs in the presence of physiological albumin concentrations.

Mots clés: MRSA; Vancomycin tolerance; Lipopeptides; Killing curves

M. Torrico, M.J. Giménez, N. González, L. Alou, D. Sevillano, et al.. Bactericidal activity of daptomycin versus vancomycin in the presence of human albumin against vancomycin-susceptible but tolerant meticillin-resistant (MRSA) with daptomycin minimum inhibitory concentrations of 1–2μg/mL. International Journal of Antimicrobial Agents, 2009, 35 (2), pp.131. ⟨10.1016/j.ijantimicag.2009.09.021⟩. ⟨hal-00556371⟩