The comparative antimicrobial activity of levofloxacin tested against 350 clinical isolates of streptococci.

The global trend of increasing tolerance and outright resistance to penicillin among streptococcal species becomes even more problematic when considering the coresistance patterns to other commonly used alternative therapies. Levofloxacin is a fluoroquinolone with excellent bioavailability properties that affords potential use in the treatment of a wide variety of infections caused by Gram-positive organisms such as streptococci. We evaluated the antistreptococcal activity (350 strains) of levofloxacin compared with other fluoroquinolones, beta-lactams (penicillin and cephalosporins), erythromycin, and vancomycin against beta- and alpha-hemolytic streptococci including penicillin-resistant strains of pneumococci and species within the viridans group. With the exception of one strain, all isolates were inhibited by levofloxacin concentrations of < or = 2 micrograms/ml including all penicillin-resistant viridans group and pneumococcal strains. This activity was superior to that of comparison fluoroquinolones, all beta-lactams, and erythromycin, whereas all strains remained susceptible to vancomycin. Time-kill results established that levofloxacin is bactericidal against most streptococci and has enhanced activity when combined with gentamicin. These results suggest that levofloxacin alone or in combination with an aminoglycoside may prove useful as an alternative to conventional therapeutic approaches of commonly encountered or serious streptococcal infections.