Open AccessPotent Antipneumococcal Activity of Gemifloxacin Is Associated with Dual Targeting of Gyrase and Topoisomerase IV, an In Vivo Target Preference for Gyrase, and Enhanced Stabilization of Cleavable Complexes In Vitro
Author(s) -
Victoria J. Heaton,
Jane E. Ambler,
L. Mark Fisher
Publication year - 2000
Publication title -
antimicrobial agents and chemotherapy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.07
H-Index - 259
eISSN - 1070-6283
pISSN - 0066-4804
DOI - 10.1128/aac.44.11.3112-3117.2000
Subject(s) - gemifloxacin , dna gyrase , topoisomerase iv , sparfloxacin , quinolone , antibacterial agent , microbiology and biotechnology , biology , streptococcus pneumoniae , mutant , ciprofloxacin , topoisomerase , chemistry , pharmacology , biochemistry , in vitro , ofloxacin , escherichia coli , antibiotics , gene
We investigated the roles of DNA gyrase and topoisomerase IV in determining the susceptibility ofStreptococcus pneumoniae to gemifloxacin, a novel fluoroquinolone which is under development as an antipneumococcal drug. Gemifloxacin displayed potent activity againstS. pneumoniae 7785 (MIC, 0.06 μg/ml) compared with ciprofloxacin (MIC, 1 to 2 μg/ml). Complementary genetic and biochemical approaches revealed the following. (i) The gemifloxacin MICs for isogenic 7785 mutants bearing eitherparC orgyrA quinolone resistance mutations were marginally higher than wild type at 0.12 to 0.25 μg/ml, whereas the presence of both mutations increased the MIC to 0.5 to 1 μg/ml. These data suggest that both gyrase and topoisomerase IV contribute significantly as gemifloxacin targets in vivo. (ii) Gemifloxacin selected first-stepgyrA mutants ofS. pneumoniae 7785 (gemifloxacin MICs, 0.25 μg/ml) encoding Ser-81 to Phe or Tyr, or Glu-85 to Lys mutations. These mutants were cross resistant to sparfloxacin (which targets gyrase) but not to ciprofloxacin (which targets topoisomerase IV). Second-step mutants (gemifloxacin MICs, 1 μg/ml) exhibited an alteration inparC resulting in changes of ParC hot spot Ser-79 to Phe or Tyr. Thus, gyrase appears to be the preferential in vivo target. (iii) Gemifloxacin was at least 10- to 20-fold more effective than ciprofloxacin in stabilizing a cleavable complex (the cytotoxic lesion) with eitherS. pneumoniae gyrase or topoisomerase IV enzyme in vitro. These data suggest that gemifloxacin is an enhanced affinity fluoroquinolone that acts against gyrase and topoisomerase IV inS. pneumoniae , with gyrase the preferred in vivo target. The marked potency of gemifloxacin against wild type and quinolone-resistant mutants may accrue from greater stabilization of cleavable complexes with the target enzymes.