Figure 2.

Intracellular action of fluoroquinolones. When DNA gyrase and DNA topoisomerase IV bind to DNA, they break both DNA strands at the interaction site. If fluoroquinolones are present, a reaction intermediate is trapped in which the DNA is broken and topoisomerase subunits are covalently bound to broken DNA. The trapped complexes block DNA synthesis and bacterial growth. Release of broken DNA in the complexes from the constraint imposed by the topoisomerases correlates with cell death (10).