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J Med Microbiol 55 (2006), 1395-1401; DOI: 10.1099/jmm.0.46636-0
© 2006 Society for General Microbiology
ISSN 1473-5644

Topoisomerase mutations and efflux are associated with fluoroquinolone resistance in Enterococcus faecalis

Yoshihiro Oyamada1, Hideaki Ito1, Matsuhisa Inoue2 and Jun-ichi Yamagishi3

1 Pharmacology Research Laboratories, Dainippon Sumitomo Pharma Co. Ltd, Enoki 33-94, Osaka 564-0053, Japan

2 Department of Environmental Infectious Disease, Graduate School of Medical Science, Kitasato University, 1-15-1 Kitasato, Sagamihara, Kanagawa 228-8555, Japan

3 Technology Research and Development Center, Dainippon Sumitomo Pharma Co. Ltd, Ebie 1-5-51, Fukushima-ku, Osaka 553-0001, Japan

Correspondence
Hideaki Ito
hideaki-ito{at}ds-pharma.co.jp

Received 20 March 2006
Accepted 29 June 2006

To understand better the mechanisms of fluoroquinolone resistance in Enterococcus faecalis, fluoroquinolone-resistant mutants isolated from Ent. faecalis ATCC 29212 by stepwise selection with sparfloxacin (SPX) and norfloxacin (NOR) were analysed. The results showed the following. (i) In general, fluoroquinolone-resistance mechanisms in Ent. faecalis are similar to those in other Gram-positive bacteria, such as Staphylococcus aureus and Streptococcus pneumoniae, namely, mutants with amino acid changes in both GyrA and ParC exhibited high fluoroquinolone resistance, and single GyrA mutants and a single ParC mutant were more resistant to SPX and NOR, respectively, than the parent strain, indicating that the primary targets of SPX and NOR in Ent. faecalis are DNA gyrase and topoisomerase IV, respectively. (ii) Alterations in GyrB ({Delta}KGA, residues 395–397) and ParE (Glu-459 to Lys) were associated with fluoroquinolone resistance in some mutants. Moreover, the facts that the NOR MIC, but not the SPX MIC, decreased in the presence of multidrug efflux pump inhibitors, that NOR accumulation decreased in the cells, and that the EmeA mRNA expression level did not change, strongly suggested that a NorA-like efflux pump, rather than EmeA, was involved in resistance to NOR.

Abbreviations: ABC, ATP-binding cassette; Acr, acriflavine; CCCP, carbonyl cyanide 3-chlorophenylhydrazone; MDR, multidrug resistance efflux pump; MF, major facilitator; NOR, norfloxacin; QRDR, quinolone resistance-determining region; SPX, sparfloxacin.






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