In vitro activity of ciprofloxacin against methicillin-susceptible and methicillin-resistant staphylococci

Ciprofloxacin was found to be active against selected strains of methicillin-resistant as well as methicillin-susceptible Staphylococcus aureus and Staphylococcus epidermidis, having minimal inhibitory concentrations <0.8 g/ml with inocula of approximately 10⁴ CFU/ml. When killing kinetic studies were done with inocula of approximately 10⁶ CFU/ml and various ciprofloxacin concentrations, the killing effect was low (<3 log₁₀ in 6h) and regrowth of the culture was seen after 24 h in at least one Staphylococcus aureus strain. After 48 h incubation, mutants with MICs eightfold that of the parental strain had grown to a number of approximately 10¹⁰ CFU/ml.