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 less than 0.8 micrograms/ml with inocula of approximately 10(4) CFU/ml. When killing kinetic studies were done with inocula of approximately 10(6) CFU/ml and various ciprofloxacin concentrations, the killing effect was low (less than 3 log10 in 6 h) 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 10(10) CFU/ml.