Topoisomerase IV is a target of quinolones in Escherichia coli

Proc Natl Acad Sci U S A. 1995 Dec 5;92(25):11801-5. doi: 10.1073/pnas.92.25.11801.


We have demonstrated that, in Escherichia coli, quinolone antimicrobial agents target topoisomerase IV (topo IV). The inhibition of topo IV becomes apparent only when gyrase is mutated to quinolone resistance. In such mutants, these antibiotics caused accumulation of replication catenanes, which is diagnostic of a loss of topo IV activity. Mutant forms of topo IV provided an additional 10-fold resistance to quinolones and prevented drug-induced catenane accumulation. Drug inhibition of topo IV differs from that of gyrase. (i) Wild-type topo IV is not dominant over the resistant allele. (ii) Inhibition of topo IV leads to only a slow stop in replication. (iii) Inhibition of topo IV is primarily bacteriostatic. These differences may result from topo IV acting behind the replication fork, allowing for repair of drug-induced lesions. We suggest that this and a slightly higher intrinsic resistance of topo IV make it secondary to gyrase as a quinolone target. Our results imply that the quinolone binding pockets of gyrase and topo IV are similar and that substantial levels of drug resistance require mutations in both enzymes.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Anti-Bacterial Agents / pharmacology*
  • Ciprofloxacin
  • DNA Gyrase
  • DNA Replication / drug effects*
  • DNA Topoisomerase IV
  • DNA Topoisomerases, Type II / drug effects*
  • DNA Topoisomerases, Type II / genetics
  • DNA, Bacterial / metabolism
  • Dose-Response Relationship, Drug
  • Drug Resistance, Microbial
  • Escherichia coli / drug effects*
  • Escherichia coli / enzymology
  • Mutation
  • Norfloxacin / pharmacology
  • Nucleic Acid Conformation
  • Quinolones / pharmacology*


  • Anti-Bacterial Agents
  • DNA, Bacterial
  • Quinolones
  • Ciprofloxacin
  • DNA Topoisomerase IV
  • DNA Gyrase
  • DNA Topoisomerases, Type II
  • Norfloxacin