Activity of ciprofloxacin against methicillin-resistant Staphylococcus aureus

Ciprofloxacin, a carboxy quinolone antibiotic with a broad spectrum of activity, was tested against 54 strains of methicillin-resistant Staphylococcus aureus. The ciprofloxacin MICs for 50 and 90% of the isolates were 0.25 and 0.5 micrograms/ml, respectively, and its MBC for 90% of the isolates was 1.0 microgram/ml. Killing kinetic studies were conducted in vitro with ciprofloxacin and vancomycin individually and in combination. The results of these studies showed that ciprofloxacin at 2 micrograms/ml and vancomycin at 10 micrograms/ml decreased the number of organisms by approximately 1.5 log10 after 6 h. The combination of ciprofloxacin plus vancomycin did not alter the rate of killing over that achieved by ciprofloxacin alone. The in vitro killing of resistant staphylococci was rapid, and the potential use of ciprofloxacin for infections caused by methicillin-resistant S. aureus should be further explored.