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Antimicrobial Agents and Chemotherapy, December 2005, p. 5051-5057, Vol. 49, No. 12
0066-4804/05/$08.00+0     doi:10.1128/AAC.49.12.5051-5057.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

DX-619, a Novel Des-Fluoro(6) Quinolone Manifesting Low Frequency of Selection of Resistant Staphylococcus aureus Mutants: Quinolone Resistance beyond Modification of Type II Topoisomerases

Jacob Strahilevitz, Que Chi Truong-Bolduc, and David C. Hooper*

Division of Infectious Diseases, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts 02114

Received 27 July 2005/ Returned for modification 28 August 2005/ Accepted 21 September 2005

DX-619, a novel des-fluoro(6) quinolone, was 16- to 32-fold, twofold, and four- to eightfold more potent than ciprofloxacin, gemifloxacin, and garenoxacin, respectively, against wild-type Staphylococcus aureus. DX-619 manifested equal fourfold increases in MIC against a common parC mutant and a common gyrA mutant and selected for mutants at up to two- to fourfold its MIC, consistent with dual-targeting properties. Of the four independent single-step mutants selected, two had new single mutations in parC (V87F and R17H), and two shared a new gyrA mutation (A26V), one with an additional deletion mutation in parE ({Delta}215-7). By allelic exchange, the ParC but not the GyrA or ParE mutation was shown to be fully responsible for the resistance phenotypes, suggesting an as yet undefined mechanism of resistance operating in conjunction with type II topoisomerase mutations contributed to resistance to DX-619. Studies with purified topoisomerase IV and gyrase from S. aureus also showed that DX-619 had similar activity against topoisomerase IV and gyrase (50% stimulation of cleavage complexes concentration, 1.25 and 0.62 to 1.25 µg/ml, respectively). Susceptibility studies with DX-619 and an array of efflux pump substrates with and without reserpine, an inhibitor of efflux pumps, suggested that resistance in DX-619-selected mutants is affected by mechanisms other than mutations in topoisomerases or known reserpine-inhibitable pumps in S. aureus and thus are likely novel.


* Corresponding author. Mailing address: Division of Infectious Diseases, Massachusetts General Hospital, 55 Fruit St., Boston, MA 02114-2696. Phone: (617) 726-3812. Fax: (617) 726-7416. E-mail: dhooper{at}partners.org.


Antimicrobial Agents and Chemotherapy, December 2005, p. 5051-5057, Vol. 49, No. 12
0066-4804/05/$08.00+0     doi:10.1128/AAC.49.12.5051-5057.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.




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