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Novel Fluoroquinolone-Modifying Enzyme: Dual Resistance Mechanism

Investigating a dual-function enzyme that modifies both aminoglycosides and fluoroquinolones, causing reduced susceptibility to ciprofloxacin. This study explores gene identification, cloning, mutagenesis, mechanism determination, phenotypic testing, and resistance potential. The enzyme AAC(6')-Ib-cr exhibits N-acetylation at the piperazinyl substituent of ciprofloxacin. The enzyme's remarkable adaptation highlights a new challenge in antimicrobial resistance.

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Novel Fluoroquinolone-Modifying Enzyme: Dual Resistance Mechanism

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  1. Fluoroquinolone-modifying enzyme: a new adaptation of a common aminoglycoside acetyltransferase Ari Robicsek, Jacob Strahilevitz, George A Jacoby Nature Medicine12, 1,January (2006) Infection disease 林建州 報告

  2. Background Peperazinyl substituent

  3. AIM Identification of a variant of an aminoglycoside-modifying enzyme, that has acquired the ability also to modify select fluoroquinolones

  4. Result • Identification of the resistance gene • Gene cloning and screening • Site –directed mutagenesis • Chemical deternination of the mechanism of resistance • Phenotypic testing • Determination of resistance-promoting potential • Population screening

  5. Integron sequence of plasmid pHSH10-2. Encoded quinolone resistance gene

  6. 4X

  7. Transformation Low level ciprofloxacin resistance

  8. Figure 1.Sequence alignment of eight different aac(6')-Ib variants and aac(6')-Ib-cr. Try102 Arg, Asp179Try

  9. Figure 2.Enzyme kinetics of AAC(6')-Ib-cr. Ecoli DH10B Acetyl transferase activity

  10. E. coli J53 pBC SK-aac(6')-Ib-cr (. ) Figure3.Mutant prevention concentration (MPC) assay. E. coli J53 (o )

  11. Summary • We describe reduced susceptibility to ciprofloxacin in clinical bacterial isolates conferred by a variant of the gene encoding aminoglycoside acetyltransferase AAC(6')-Ib. • This enzyme reduces the activity of ciprofloxacin by N-acetylation at the amino nitrogen on its piperazinyl substituent • a single-function resistance enzyme has crossed class boundaries, and is now capable of enzymatically undermining two unrelated antimicrobial agents, one of them fully synthetic.

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