In vitro activity of daptomycin combined with dalbavancin and linezolid, and dalbavancin with linezolid against MRSA strains.

Abstract Combination therapies have a distinct advantage over monotherapies in terms of their broad spectrum, synergistic effect and prevention of the emergence of drug resistance. In the present study, the in vitro antibacterial activity of daptomycin combinations with linezolid and dalbavancin, and dalbavancin with linezolid were evaluated against 30 clinical MRSA strains. The MICs of all antibiotics were determined using microbroth dilution as described by the CLSI. The in vitro activities of antibiotics in combination were assessed by using a microbroth 'chequerboard' assay. The MIC values of all antibiotics determined were evaluated in accordance with the recommendations of the CLSI for daptomycin and linezolid, and the FDA for dalbavancin. All strains (100%) were found to be susceptible to daptomycin, dalbavancin and linezolid. The MIC50, MIC90 and MICrange values of these antibiotics were determined to be 1, 1 and 0.5-1 mg/L, 0.12, 0.12 and 0.03-0.12 mg/L, and 1, 2 and 1-2 mg/L, respectively. The rates of synergistic effects were 67% for daptomycin combined with dalbavancin and with linezolid, and 60% for dalbavancin combined with linezolid. The results of this study show that in vitro combinations of these new antimicrobials will be effective in the therapy of MRSA infections.