Topoisomerase mutations and efflux are associated with fluoroquinolone resistance in Enterococcus faecalis.
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 (DeltaKGA, 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.
Oyamada
Yoshihiro
Y
Pharmacology Research Laboratories, Dainippon Sumitomo Pharma Co. Ltd, Enoki 33-94, Osaka 564-0053, Japan.
Ito
Hideaki
H
Pharmacology Research Laboratories, Dainippon Sumitomo Pharma Co. Ltd, Enoki 33-94, Osaka 564-0053, Japan.
Inoue
Matsuhisa
M
Department of Environmental Infectious Disease, Graduate School of Medical Science, Kitasato University, 1-15-1 Kitasato, Sagamihara, Kanagawa 228-8555, Japan.
Yamagishi
Jun-Ichi
JI
Technology Research and Development Center, Dainippon Sumitomo Pharma Co. Ltd, Ebie 1-5-51, Fukushima-ku, Osaka 553-0001, Japan.
D000890:Anti-Infective Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics*; D027081:DNA Gyrase / Q000235:genetics*; D027101:DNA Topoisomerase IV / Q000235:genetics*; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D013293:Enterococcus faecalis / Q000187:drug effects* / Q000235:genetics; D024841:Fluoroquinolones / Q000494:pharmacology*; D026901:Membrane Transport Proteins / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D009643:Norfloxacin / Q000494:pharmacology*; D017354:Point Mutation
D000890:Anti-Infective Agents; D001426:Bacterial Proteins; C445688:EmeA protein, Enterococcus faecalis; D024841:Fluoroquinolones; D026901:Membrane Transport Proteins; D027101:DNA Topoisomerase IV; D027081:DNA Gyrase; D009643:Norfloxacin; C061363:sparfloxacin