Inhibition of Enzymatic Acetylation-Mediated Resistance to Plazomicin by Silver Ions

Abstract

Plazomicin is a recent U.S. Food and Drug Administration (FDA)-approved semisynthetic aminoglycoside. Its structure consists of a sisomicin scaffold modified by adding a 2(S)-hydroxy aminobutyryl group at the N1 position and a hydroxyethyl substituent at the 6′ position. These substitutions produced a molecule refractory to most aminoglycoside-modifying enzymes. The main enzyme within this group that recognizes plazomicin as substrate is the aminoglycoside 2′-N-acetyltransferase type Ia [AAC(2′)-Ia], which reduces the antibiotic’s potency. Designing formulations that combine an antimicrobial with an inhibitor of resistance is a recognized strategy to extend the useful life of existing antibiotics. We have recently found that several metal ions inhibit the enzymatic inactivation of numerous aminoglycosides mediated by the aminoglycoside 6′-N-acetyltransferase type Ib [AAC(6′)-Ib]. In particular, Ag+, which also enhances the effect of aminoglycosides by other mechanisms, is very effective in interfering with AAC(6′)-Ib-mediated resistance to amikacin. Here we report that silver acetate is a potent inhibitor of AAC(2′)-Ia-mediated acetylation of plazomicin in vitro, and it reduces resistance levels of Escherichia coli carrying aac(2′)-Ia. The resistance reversion assays produced equivalent results when the structural gene was expressed under the control of the natural or the blaTEM-1 promoters. The antibiotic effect of plazomicin in combination with silver was bactericidal, and the mix did not show significant toxicity to human embryonic kidney 293 (HEK293) cells.

Dynamics and quantitative contribution of the aminoglycoside 6′- N -acetyltransferase type Ib to amikacin resistance

“…Total soluble proteins (enzymatic extracts) were prepared as before ( 49 ). Briefly, cells were pelleted from cultures by centrifugation and resuspended in a 0.5 mM MgCl 2 solution.…”

Dynamics and quantitative contribution of the aminoglycoside 6′-N-acetyltransferase type Ib [AAC(6′)-Ib] to amikacin resistance

“…Total soluble proteins (enzymatic extracts) were prepared as before (48). Briefly, cells were pelleted from cultures by centrifugation and resuspended in a 0.5 mM MgCl2 solution.…”