Purification of pneumococcal type II topoisomerases and inhibition by gemifloxacin and other quinolones

Topoisomerase IV and DNA gyrase were purified from a ciprofloxacin-sensitiv e Streptococcus pneumoniae strain and from two clinical isolates of S. pneu moniae with high-level resistance to ciprofloxacin by means of a gene cloni ng method in Escherichia coil. All the quinolones tested (gemifloxacin, tro vafloxacin, levofloxacin, ciprofloxacin and grepafloxacin) were able to inh ibit topoisomerase IV at lower concentrations than those required for DNA g yrase, suggesting that topoisomerase IV is the primary target in the three pneumococci, in agreement with recently published enzyme data. Gemifloxacin (SB-265805) was found to be the most active agent against topoisomerase IV but, surprisingly, not against DNA gyrase, These findings indicate that th e potent in vitro activity of gemifloxacin against S. pneumoniae, including ciprofloxacin-resistant strains, results from a strong affinity for pneumo coccal topoisomerase IV.