Inhibition of Aminoglycoside 6′-N-Acetyltransferase Type Ib by Zinc: Reversal of Amikacin Resistance in Acinetobacter baumannii and Escherichia coli by a Zinc Ionophore

In vitro activity of the aminoglycoside 6′-N-acetyltransferase type Ib [AAC(6′)-Ib] was inhibited by ZnCl2 with a 50% inhibitory concentration (IC50) of 15 μM. Growth of Acinetobacter baumannii or Escherichia coli harboring aac(6′)-Ib in cultures containing 8 μg/ml amikacin was significantly inhibited by the addition of 2 μM Zn2+ in complex with the ionophore pyrithione (ZnPT).