 This mechanism involved disabling the bacterial topoisomerase II/IV enzyme (the target in most Gram-positive bacteria) or DNA gyrase (the target in Gram-negative bacteria), preventing the bacteria from unwinding their DNA and undergoing either DNA replication or transcription.The majority of drugs in clinical use are actually quinoline derivatives that belong to the subset fluoroquinolones, which have a fluorine atom attached to the central ring system, often at the C-6 or C-7 position.There are also many non-antibacterial medical uses for 4-hydroxyquinoline.