JAC Advance Access originally published online on January 15, 2009
Journal of Antimicrobial Chemotherapy 2009 63(3):443-450; doi:10.1093/jac/dkn528
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Original research |
Target specificity of the new fluoroquinolone besifloxacin in Streptococcus pneumoniae, Staphylococcus aureus and Escherichia coli
1 Université Paris12, IFR10, F-94010 Creteil, France 2 AP-HP, Groupe Hospitalier Albert Chenevier-Henri Mondor, Service de Bactériologie-Virologie-Hygiène, F-94010 Créteil Cedex, France 3 Université Pierre et Marie Curie Paris6, EA1541, Service de Bactériologie-Hygiène, F-75006 Paris, France 4 St George’s, University of London, Molecular and Metabolic Signalling Centre, Division of Basic Medical Sciences, London SW17 ORE, UK 5 AP-HP, CHU Pierre et Marie Curie site Pitié Salpêtrière, F-75634 Paris Cedex 13, France 6 Laboratoires Bausch and Lomb/Chauvin, 34961 Montpellier Cedex 2, France
Received 14 August 2008; returned 14 October 2008; revised 7 December 2008; accepted 10 December 2008
* Corresponding author. Present address: Laboratoire de Microbiologie, Hôpital Saint Louis, 1 avenue Claude Vellefaux, 75475 Paris Cedex 10, France. Tel: +33-1-42499348; Fax: +33-1-42499200; E-mail: emmanuelle.cambau{at}sls.aphp.fr
Objectives: Besifloxacin is a new fluoroquinolone in development for ocular use. We investigated its mode of action and resistance in two major ocular pathogens, Streptococcus pneumoniae and Staphylococcus aureus, and in the reference species Escherichia coli.
Methods: Primary and secondary targets of besifloxacin were evaluated by: (i) mutant selection experiments; (ii) MIC testing of defined topoisomerase mutants; and (iii) inhibition and cleavable complex assays with purified S. pneumoniae and E. coli DNA gyrase and topoisomerase IV enzymes.
Results: Enzyme assays showed similar besifloxacin activity against S. pneumoniae gyrase and topoisomerase IV, with IC50 and CC25 of 2.5 and 1 µM, respectively. In contrast to ciprofloxacin and moxifloxacin, besifloxacin was equally potent against both S. pneumoniae and E. coli gyrases. DNA gyrase was the primary target in all three species, with substitutions observed at positions 81, 83 and 87 in GyrA and 426 and 466 in GyrB (E. coli numbering). Topoisomerase IV was the secondary target. Notably, resistant mutants were not recovered at 4-fold besifloxacin MICs for S. aureus and S. pneumoniae, and S. aureus topoisomerase mutants were only obtained after serial passage in liquid medium. Besifloxacin MICs were similarly affected by parC or gyrA mutations in S. aureus and S. pneumoniae and remained below 1 mg/L in gyrA–parC double mutants.
Conclusions: Although mutant selection experiments indicated that gyrase is a primary target, further biochemical and genetic studies showed that besifloxacin has potent, relatively balanced activity against both essential DNA gyrase and topoisomerase IV targets in S. aureus and S. pneumoniae.
Keywords: gyrase , topoisomerase IV , pneumococci , staphylococci , resistant mutant
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  W. Haas, C. M. Pillar, G. E. Zurenko, J. C. Lee, L. S. Brunner, and T. W. Morris Besifloxacin, a Novel Fluoroquinolone, Has Broad-Spectrum In Vitro Activity against Aerobic and Anaerobic Bacteria Antimicrob. Agents Chemother., August 1, 2009; 53(8): 3552 - 3560. [Abstract] [Full Text] [PDF]
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