Dalbavancin

MICs of vancomycin (Sigma-Aldrich, St. Louis, MO, USA), teicoplanin (Sigma-Aldrich, USA), and dalbavancin (kindly gifted by Sanofi, Italy) toward S. aureus were determined by the broth dilution method, according to the guidelines of the Clinical and Laboratory Standards Institute [57 ]. The antibiotics were prepared by dissolving the corresponding powder in deionized water, filtered with a cut-off of 0.22 µm, and finally brought to appropriate dilution with MHB2. Ca. 5.0 × 10⁵ bacterial cells in exponential growth were inoculated in MHB2, together with increasing concentrations of the antibiotics. MICs were defined as the minimal antibiotic concentration at which no turbidity could be detected after incubation for 20 h at 37 °C and 200 rpm. For calculating MBCs, 0.1 mL of bacterial cultures used for the MIC test were plated on MHA (Müller Hinton Agar, VWR International S.r.l., USA), then incubated at 37 °C for 24 h. MBCs were the lowest antibiotic concentrations, at which no growth could be observed.

MICs of vancomycin (Sigma-Aldrich, St. Louis, MO, USA), teicoplanin (Sigma-Aldrich), and dalbavancin (kindly provided by Sanofi, Brindisi, Italy) towards S. epidermidis strain 4 were determined by the broth dilution method, following Clinical and Laboratory Standards Institute guidelines [29 ]. A total of 5 × 10⁵ viable bacterial cells were inoculated into MHB2 medium (VWR International Srl) in 96-well plates and supplemented with increasing antibiotic concentrations (from 0 to 128 µg/mL) up to 100 µL final volume. Plates were then incubated for 16–20 h at 37 °C and 100 rpm. MIC was defined as the minimal concentration of antibiotic at which no turbidity could be detected. For MBC determination, bacterial cultures used for the MIC test were plated onto Müller–Hinton Agar (MHA; VWR International Srl) and incubated at 37 °C for 24 h. MBC was defined as the lowest concentration of antibiotic at which no visible growth was detected on plates. All experiments were performed at least in triplicate.