Journal Article

Type II topoisomerase mutations in <i>Bacillus anthracis</i> associated with high-level fluoroquinolone resistance

Darrin J. Bast, Abed Athamna, Carla L. Duncan, Joyce C. S. de Azavedo, Donald E. Low, Galia Rahav, David Farrell and Ethan Rubinstein

in Journal of Antimicrobial Chemotherapy

Published on behalf of British Society for Antimicrobial Chemotherapy

Volume 54, issue 1, pages 90-94
Published in print July 2004 | ISSN: 0305-7453
Published online July 2004 | e-ISSN: 1460-2091 | DOI:
Type II topoisomerase mutations in Bacillus anthracis associated with high-level fluoroquinolone resistance

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Objectives: To identify and characterize the mechanisms of high-level fluoroquinolone resistance in two strains of Bacillus anthracis following serial passage in increasing concentrations of fluoroquinolones.

Methods: Fluoroquinolone-resistant isolates of the Sterne and Russian Anthrax Vaccine STi strains were obtained following serial passage in the presence of increasing concentrations of four different fluoroquinolones. The quinolone-resistance-determining regions of the type II topoisomerase genes from the resistant strains were amplified by PCR and characterized by DNA sequence analysis. The MICs in the presence and absence of reserpine were determined using broth microdilution as a means of detecting active efflux.

Results: Single and double amino acid substitutions in the GyrA (Ser-85-Leu; Glu-89-Arg/Gly/Lys) and GrlA (Ser-81-Tyr; Val-96-Ala; Asn-70-Lys) were most common. A single amino acid substitution in GyrB (Asp-430-Asn) was also identified. Efflux only applied to isolates selected for by either levofloxacin or ofloxacin.

Conclusions: Specific amino acid substitutions in the type II topoisomerase enzymes significantly contributed to the development of high-level fluoroquinolone resistance in B. anthracis. However, notable differences between the strains and the drugs tested were identified including the role of efflux and the numbers and types of mutations identified.

Keywords: anthrax; DNA gyrase; topoisomerase IV

Journal Article.  2858 words. 

Subjects: Medical Oncology ; Critical Care

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