title: Effects of ciprofloxacin on plasmid DNA supercoiling of Escherichia coli topoisomerase I and gyrase mutants.
abstract: Changes in plasmid DNA supercoiling were measured following treatment of Escherichia coli cells, carrying topoisomerase mutations, with the quinolone ciprofloxacin. In quinolone-susceptible cells (top+ gyr+) as well as in topA mutants and in gyrB mutants, plasmid DNA was relaxed after the addition of ciprofloxacin. In cells partially resistant to quinolones, low ciprofloxacin levels led to an increase in negative superhelicity of plasmid DNA, whereas at higher ciprofloxacin concentrations, DNA became relaxed. Cells exhibiting partial resistance to quinolones carried either a gyrA mutation alone or a combination of gyrA and gyrB mutations. Moreover, they showed a reduction in gyrase activity, indicated by the supercoiling of a reporter plasmid. Therefore, we conclude that a low level of quinolone action and a DNA with a lower-than-normal level of superhelicity are the two essential conditions for obtaining a ciprofloxacin-promoted increase in plasmid DNA supercoiling. In contrast, deficiency in topoisomerase I is not required for this effect.
authors.affiliation: Instituto de Investigaciones Citológicas de la Caja de Ahorros de Valencia, Spain.
authors.forename: V
authors.initials: V
authors.lastname: Aleixandre
authors.forename: G
authors.initials: G
authors.lastname: Herrera
authors.forename: A
authors.initials: A
authors.lastname: Urios
authors.forename: M
authors.initials: M
authors.lastname: Blanco
mesh_terms: D002939:Ciprofloxacin / Q000494:pharmacology*; D004264:DNA Topoisomerases, Type I / Q000235:genetics / Q000378:metabolism*; D004250:DNA Topoisomerases, Type II / Q000235:genetics / Q000378:metabolism*; D004278:DNA, Superhelical / Q000187:drug effects*; D004352:Drug Resistance, Microbial / Q000235:genetics; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D009154:Mutation; D009690:Nucleic Acid Conformation / Q000187:drug effects*; D010957:Plasmids; D011804:Quinolines / Q000494:pharmacology
chemical_list: D004278:DNA, Superhelical; D011804:Quinolines; D002939:Ciprofloxacin; C037219:quinoline; D004264:DNA Topoisomerases, Type I; D004250:DNA Topoisomerases, Type II