Moxifloxacin

Antimicrobial susceptibility of the SAR Bari strain was determined by a BD PHOENIX^™ 100 instrument (Becton Dickinson, Franklyn Lake, NJ). Data were elaborated by the BD Epicenter Expert System according to EUCAST rules (http://www.eucast.org). The PMIC/ID-88 (BD) panel was used to test susceptibility to ampicillin, cefoxitin, ceftaroline, ciprofloxacin, clindamycin, daptomycin, erythro-mycin, fosfomycin, fusidic acid, gentamicin, imipenem, linezolid, moxifloxacin, mupirocin, nitro-furantoin, oxacillin, penicillin, rifampin, teicoplanin, tetracyclin, tigecycline, trimethoprim/ sulfamethoxazole, and vancomycin. The Epsilometer Test (ETest) was used for testing resistance to ciprofloxacin, daptomycin, erythromycin, gentamicin, moxifloxacin, tetracyclin, tigecycline, trimethoprim/sulfamethoxazole, and vancomycin (bioMérieux, Marcy-L’Étolie, France and Liofilchem, Roseto degli Abruzzi, Italy). All tests were repeated on four independent technical replicates. MIC interpretative breakpoints were defined according to EUCAST recommendations. Staphylococcus aureus ATCC 29213 was used as a control strain.

To determine MIC of cells on agar plates, 100 µL of strains grown in ThyB to OD₆₂₀ ~0.4 was plated and a levofloxacin, ciprofloxacin, or moxifloxacin E-test strip (bioMerieux) was added onto the center of each plate. MIC (µg/mL) was determined to be the concentration at which the symmetrical inhibition ellipse edge intersects the E-test strips on the plate (81 (link)). To determine MIC of cells in broth, titered frozen stocks were diluted 1:100 in C+Y with increasing concentrations of antibiotic (0–4 µg/mL for levofloxacin and 0–8 µg/mL for ciprofloxacin) in a 96-well plate. OD₆₂₀ of cultures was monitored using Biotek Cytation 3 plate reader over 24 h.