title: Nonoptimal DNA topoisomerases allow maintenance of supercoiling levels and improve fitness of Streptococcus pneumoniae.
abstract: Fluoroquinolones, which target gyrase and topoisomerase IV, are used for treating Streptococcus pneumoniae infections. Fluoroquinolone resistance in this bacterium can arise via point mutation or interspecific recombination with genetically related streptococci. Our previous study on the fitness cost of resistance mutations and recombinant topoisomerases identified GyrAE85K as a high-cost change. However, this cost was compensated for by the presence of a recombinant topoisomerase IV (parC and parE recombinant genes) in strain T14. In this study, we purified wild-type and mutant topoisomerases and compared their enzymatic activities. In strain T14, both gyrase carrying GyrAE85K and recombinant topoisomerase IV showed lower activities (from 2.0- to 3.7-fold) than the wild-type enzymes. These variations of in vitro activity corresponded to changes of in vivo supercoiling levels that were analyzed by two-dimensional electrophoresis of an internal plasmid. Strains carrying GyrAE85K and nonrecombinant topoisomerases had lower (11.1% to 14.3%) supercoiling density (σ) values than the wild type. Those carrying GyrAE85K and recombinant topoisomerases showed either partial or total supercoiling level restoration, with σ values being 7.9% (recombinant ParC) and 1.6% (recombinant ParC and recombinant ParE) lower than those for the wild type. These data suggested that changes acquired by interspecific recombination might be selected because they reduce the fitness cost associated with fluoroquinolone resistance mutations. An increase in the incidence of fluoroquinolone resistance, even in the absence of further antibiotic exposure, is envisaged.
authors.affiliation: Unidad de Genética Bacteriana, Centro Nacional de Microbiología, Instituto de Salud Carlos III, Carretera a Pozuelo Km 2, 28220 Majadahonda, Madrid, Spain.
authors.forename: Luz
authors.initials: L
authors.lastname: Balsalobre
authors.forename: María José
authors.initials: MJ
authors.lastname: Ferrándiz
authors.forename: Gabriela
authors.initials: G
authors.lastname: de Alba
authors.forename: Adela G
authors.initials: AG
authors.lastname: de la Campa
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D027081:DNA Gyrase / Q000235:genetics / Q000378:metabolism; D026942:DNA Topoisomerases / Q000235:genetics / Q000378:metabolism*; D004250:DNA Topoisomerases, Type II / Q000235:genetics / Q000378:metabolism; D015180:Electrophoresis, Gel, Two-Dimensional; D024841:Fluoroquinolones / Q000494:pharmacology; D013296:Streptococcus pneumoniae / Q000187:drug effects / Q000201:enzymology*
chemical_list: D000900:Anti-Bacterial Agents; D024841:Fluoroquinolones; D026942:DNA Topoisomerases; D027081:DNA Gyrase; D004250:DNA Topoisomerases, Type II