The aminocoumarins novobiocin, clorobiocin and coumermycin A1are structurally related antibioticsproduced by different Streptomyces strains. They are potent inhibitors of bacterial gyrase. Their bindingsites and their mode of action differ from those of fluoroquinolones such as ciprofloxacin. Novobiocinhas been introduced into clinical use against Staphylococcus aureus infections, and S. aureus gyrase isparticularly sensitive to inhibition by aminocoumarins, while topoisomerase IV is much less sensitive.Modern genetic techniques have allowed the engineering of the producer strains, resulting in a diverserange of new aminocoumarins, including compounds which are more active than the natural antibioticsas well as a compound which is actively imported across the cell envelope of Gram-negative bacteria.A further group of aminocoumarins are the simocyclinones which bind simultaneously to two differentsites of gyrase and show a completely new mode of inhibition. Both the simocyclinones and the “clas-sical” aminocoumarins strongly inhibit the fluoroquinolone-induced activation of RecA and thereby theSOS response in S. aureus. Therefore, a combination of aminocoumarins and fluoroquinolones stronglyreduced the risk of resistance development and may offer new prospects in anti-infective therapy