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Antimicrobial Agents and Chemotherapy, September 2003, p. 2831-2837, Vol. 47, No. 9
0066-4804/03/$08.00+0     DOI: 10.1128/AAC.47.9.2831-2837.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Role of AcrR and RamA in Fluoroquinolone Resistance in Clinical Klebsiella pneumoniae Isolates from Singapore

T. Schneiders,1 S. G. B. Amyes,2 and S. B. Levy1,3*

Department of Molecular Biology and Microbiology,1 Department of Medicine, Center for Adaptation Genetics and Drug Resistance, Tufts University School of Medicine, Boston, Massachusetts 02111,3 University of Edinburgh Medical School, Edinburgh EH8 9AG, United Kingdom2

Received 5 February 2003/ Returned for modification 7 April 2003/ Accepted 5 June 2003

The MICs of ciprofloxacin for 33 clinical isolates of K. pneumoniae resistant to extended-spectrum cephalosporins from three hospitals in Singapore ranged from 0.25 to >128 µg/ml. Nineteen of the isolates were fluoroquinolone resistant according to the NCCLS guidelines. Strains for which the ciprofloxacin MIC was >=0.5 µg/ml harbored a mutation in DNA gyrase A (Ser83->Tyr, Leu, or IIe), and some had a secondary Asp87->Asn mutation. Isolates for which the MIC was 16 µg/ml possessed an additional alteration in ParC (Ser80->IIe, Trp, or Arg). Tolerance of the organic solvent cyclohexane was observed in 10 of the 19 fluoroquinolone-resistant strains; 3 of these were also pentane tolerant. Five of the 10 organic solvent-tolerant isolates overexpressed AcrA and also showed deletions within the acrR gene. Complementation of the mutated acrR gene with the wild-type gene decreased AcrA levels and produced a two- to fourfold reduction in the fluoroquinolone MICs. None of the organic solvent-tolerant clinical isolates overexpressed another efflux-related gene, acrE. While marA and soxS were not overexpressed, another marA homologue, ramA, was overexpressed in 3 of 10 organic solvent-tolerant isolates. These findings indicate that multiple target and nontarget gene changes contribute to fluoroquinolone resistance in K. pneumoniae. Besides AcrR mutations, ramA overexpression (but not marA or soxS overexpression) was related to increased AcrAB efflux pump expression in this collection of isolates.

* Corresponding author. Mailing address: Center for Adaptation Genetics and Drug Resistance, Tufts University School of Medicine, 136 Harrison Ave., Boston, MA 02111. Phone: (617) 636-6764. Fax: (617) 636-0458. E-mail: stuart.levy{at}tufts.edu.

Antimicrobial Agents and Chemotherapy, September 2003, p. 2831-2837, Vol. 47, No. 9
0066-4804/03/$08.00+0     DOI: 10.1128/AAC.47.9.2831-2837.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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