Bactericidal activity of gemifloxacin and other quinolones against Streptococcus pneumoniae

This study compared the bactericidal activity of gemifloxacin (SB-265805) a nd a panel of test quinolones against two ciprofloxacin-resistant pneumococ cal strains (Streptococcus pneumoniae 502226 and 503244) and one ciprofloxa cin-sensitive strain (S. pneumoniae C3LN4). Activities were compared by cal culating the bactericidal index of these agents. Gemifloxacin was found to be the most bactericidal quinolone tested against these strains. This findi ng confirms previous data indicating the superior in vitro activity of gemi floxacin against pneumococci, including ciprofloxacin-resistant strains. Al though both ciprofloxacin-resistant strains tested had similar quinolone MI Cs, they differed considerably in their susceptibility to the bactericidal action of these agents. S. pneumoniae 502226 was more readily killed by qui nolones than S. pneumoniae 503244 but, as would be expected, both were less susceptible than the ciprofloxacin-sensitive strain. Of the quinolones tes ted, trovafloxacin showed disproportionally poor activity against the cipro floxacin-resistant strains even though potent activity was present against the ciprofloxacin-sensitive strain. These data highlight the importance of assessing quinolone bactericidal activity in addition to the MIC when evalu ating new members of this antimicrobial class.