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Antimicrobial Agents and Chemotherapy, August 2002, p. 2582-2587, Vol. 46, No. 8
0066-4804/02/$04.00+0     DOI: 10.1128/AAC.46.8.2582-2587.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

DNA Gyrase and Topoisomerase IV Mutations Associated with Fluoroquinolone Resistance in Proteus mirabilis

L. M. Weigel,* G. J. Anderson, and F. C. Tenover

Division of Healthcare Quality Promotion, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia 30333

Received 18 September 2001/ Returned for modification 30 November 2001/ Accepted 8 May 2002

Mutations associated with fluoroquinolone resistance in clinical isolates of Proteus mirabilis were determined by genetic analysis of the quinolone resistance-determining region (QRDR) of gyrA, gyrB, parC, and parE. This study included the P. mirabilis type strain ATCC 29906 and 29 clinical isolates with reduced susceptibility (MIC, 0.5 to 2 µg/ml) or resistance (MIC, >=4 µg/ml) to ciprofloxacin. Susceptibility profiles for ciprofloxacin, clinafloxacin, gatifloxacin, gemifloxacin, levofloxacin, moxifloxacin, and trovafloxacin were correlated with amino acid changes in the QRDRs. Decreased susceptibility and resistance were associated with double mutations involving both gyrA (S83R or -I) and parC (S80R or -I). Among these double mutants, MICs of ciprofloxacin varied from 1 to 16 µg/ml, indicating that additional factors, such as drug efflux or porin changes, also contribute to the level of resistance. For ParE, a single conservative change of V364I was detected in seven strains. An unexpected result was the association of gyrB mutations with high-level resistance to fluoroquinolones in 12 of 20 ciprofloxacin-resistant isolates. Changes in GyrB included S464Y (six isolates), S464F (three isolates), and E466D (two isolates). A three-nucleotide insertion, resulting in an additional lysine residue between K455 and A456, was detected in gyrB of one strain. Unlike any other bacterial species analyzed to date, mutation of gyrB appears to be a frequent event in the acquisition of fluoroquinolone resistance among clinical isolates of P. mirabilis.


* Corresponding author. Mailing address: DHQP, Anti-infectives Section (G-08), Centers for Disease Control and Prevention, 1600 Clifton Rd., N.E., Atlanta, GA 30333. Phone: (404) 639-1497. Fax: (404) 639-1381. E-mail: lweigel{at}cdc.gov.


Antimicrobial Agents and Chemotherapy, August 2002, p. 2582-2587, Vol. 46, No. 8
0066-4804/02/$04.00+0     DOI: 10.1128/AAC.46.8.2582-2587.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.




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