Bactericidal activity of quinolones against Streptococcus pneumoniae by time-kill methodology.

The increase in Streptococcus pneumoniae strains resistant to the drugs traditionally used in treatment has made the search for alternative agents necessary. We studied the bactericidal activity of ciprofloxacin, ofloxacin, levofloxacin, sparfloxacin, and trovafloxacin against six penicillin-resistant Streptococcus pneumoniae strains, using time-kill methodology. Our results indicate that trovafloxacin and sparfloxacin had greater bactericidal activity than ciprofloxacin, ofloxacin, and levofloxacin against all the strains tested, since these two quinolones showed bactericidal activity against all six strains at concentrations of not more than 4 mg/l. Ciprofloxacin and levofloxacin did not have bactericidal activity, in the range of concentrations of antibiotics used, against any of the strains studied; when such activity did exist, the concentration of antibiotic used was higher.