Inhibition of aminoglycoside 6'-N-acetyltransferase type Ib-mediated amikacin resistance in Klebsiella pneumoniae by zinc and copper pyrithione

Abstract

The in vitro activity of the aminoglycoside 6'-N-acetyltransferase type Ib [AAC(6')-Ib] was inhibited by CuCl2 with a 50% inhibitory concentration (IC50) of 2.8 μM. The growth of an amikacin-resistant Klebsiella pneumoniae strain isolated from a neonate with meningitis was inhibited when amikacin was supplemented by the addition of Zn(2+) or Cu(2+) in complex with the ionophore pyrithione. Coordination complexes between cations and ionophores could be developed for their use, in combination with aminoglycosides, to treat resistant infections.

FIG 1

Effect of copper on acetylation of AMK catalyzed by AAC(6′)-Ib. (A) Acetylating activity of AAC(6′)-Ib in the presence of different cations. Compounds were added at the indicated concentrations, and the activity was compared to that observed in the absence of additions (bar C). MgCl₂ and CaCl₂ were known not to inhibit the reaction and were tested as controls. (B) The percentage of acetylating activity of AMK by AAC(6′)-Ib was calculated for reaction mixtures containing different concentrations of CuCl₂.

FIG 2

Comparison of the effects of ZnPT and CuPT on resistance to AMK. K. pneumoniae JHCK1 cells were cultured in 100 μl Mueller-Hinton broth in microtiter plates at 37°C with the additions indicated in the figure, and the OD₆₀₀ was periodically determined. The panels show the effect on cell growth of addition of ZnPT (A and B) or CuPT (C and D) in the presence (B and D) or absence (A and C) of 16 μg/ml AMK.