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Antimicrobial Agents and Chemotherapy, August 1999, p. 2000-2004, Vol. 43, No. 8
0066-4804/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Contribution of Topoisomerase IV and DNA Gyrase Mutations in Streptococcus pneumoniae to Resistance to Novel Fluoroquinolones

Ekaterina Pestova,1,* Rebecca Beyer,1 Nicholas P. Cianciotto,2 Gary A. Noskin,1,3 and Lance R. Peterson1,3

Department of Pathology,1 Department of Microbiology,2 and Department of Medicine,3 Northwestern University Medical School, Chicago, Illinois 60611

Received 16 December 1998/Returned for modification 3 March 1999/Accepted 9 June 1999

In this study, we assessed the activity of ciprofloxacin, levofloxacin, sparfloxacin, and trovafloxacin against clinical isolates of Streptococcus pneumoniae that were resistant to the less-recently developed fluoroquinolones by using defined amino acid substitutions in DNA gyrase and topoisomerase IV. The molecular basis for resistance was assessed by using mutants selected with trovafloxacin, ciprofloxacin, and levofloxacin in vitro. This demonstrated that the primary target of trovafloxacin in S. pneumoniae is the ParC subunit of DNA topoisomerase IV, similar to most other fluoroquinolones. However, first-step mutants bearing the Ser79right-arrowPhe/Tyr substitution in topoisomerase IV subunit ParC were susceptible to trovafloxacin with a minimum inhibitory concentration of 0.25 µg/ml, and mutations in the structural genes for both topoisomerase IV subunit ParC (parC) and the DNA gyrase subunit (gyrA) were required to achieve levels of resistance above the breakpoint. The data also suggest that enhanced activity of trovafloxacin against pneumococci is due to a combination of factors that may include reduced efflux of this agent and an enhanced activity against both DNA gyrase and topoisomerase IV.

* Corresponding author. Mailing address: Department of Pathology, Ward Building, 6-223, 303 E. Chicago Ave., Chicago, IL 60611. Phone: (312) 503-8188. Fax: (312) 908-4137. E-mail: evp606{at}anima.nums.nwu.edu.

Antimicrobial Agents and Chemotherapy, August 1999, p. 2000-2004, Vol. 43, No. 8
0066-4804/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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