Antibiotic suceptibility of Rhodococcus equi

Antibiotics were dissolved in appropriate solvents and diluted in sterile distilled water to prepare stock solutions following the guidelines by Clinical and Laboratory Standards Institute (35). Minimum inhibitory concentrations of the fourteen isolates of R. equi were obtained by the microdilution broth technique (35).

Serial two-fold dilutions of the antimicrobial agents were prepared from the stock solution with concentrations ranged from 0.03 to 128 mg/L for all antibiotics. Serial dilutions were prepared using cation-adjusted Mueller–Hinton broth with 2.5% defibrinated horse blood. Inocula were produced by diluting the overnight culture of R. equi in cation-adjusted Mueller–Hinton broth with a buffered saline solution to a density of 0.5 on McFarland Turbidity Scale.