Silver Resistance In Acinetobacter baumannii BL54 Occurs Through Binding to a Ag-Binding Protein

Abstract

The mechanism of plasmid mediated silver (Ag) resistance was investigated in Acinetobacter baumannii<br />BL54. The intracellular accumulation of Ag in both original strain BL54 and Escherichia coli K12<br />transconjugant containing plasmid pUPI276 began immediately and reached a maximum within 60 minutes.<br />This initial accumulation was followed by net loss of Ag which reached a maximum within 180 min.<br />Pre-treatment of cells with 0.5 mM 2,4 dinitrophenol (DNP); 20 mM N, N-dicyclohexylcarbodiimide<br />(DCCD); 3% toluene; 25 mg/ml cefotaxime and polymyxin-B resulted in considerable decrease in the<br />accumulation process. Ags plasmid less cured derivative (BL54.1) also accumulated silver but only onefourth<br />the amount compared to the resistant strain BL54. The intracellular accumulated silver is detoxified<br />by binding to a cysteine rich metal binding protein.<br />The purified Ag-binding protein exhibited maximum absorption at 280/215 nm. From the above data<br />it could be concluded that the intracellular detoxification of silver in A. baumannii BL54 is achieved<br />through binding to a cysteine rich metalloprotein.<br /><br />