Interaction of Silver(I) Ions with the Respiratory Chain ofEscherichia coli: An Electrochemical and Scanning Electrochemical Microscopy Study of the Antimicrobial Mechanism of Micromolar Ag+

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Abstract
Electrochemical techniques were used to study the behavior of Escherichia coli on the addition of ≤10 μM AgNO3. Respiration in the presence of glucose was measured using a Clark ultramicroelectrode to determine the oxygen concentration as a function of time. The rate of respiration increased initially upon the addition of silver(I) because of the uncoupling of the respiratory chain, followed by cessation of respiration. The toxicity of 1 μM AgNO3, as determined by the time until respiration ceased, increased in the absence of glucose and in the presence of K+. The uptake of 1 μM Ag+, measured from the stripping peak height of Ag electrodeposited on a 25 μm Pt ultramicroelectrode, showed a fastest uptake in the presence of glucose, although glucose was not required for uptake. Efflux of Ag+ from cells was also detected in the presence of glucose. Scanning electrochemical microscopy (SECM) was used to follow the uptake of 1 μM Ag+ by living and dead E. coli immobilized on a glass slide coated with poly-l-lysine. Ferricyanide was used as an alternative electron acceptor to oxygen to probe the site of inhibition of Ag+ in the respiratory chain.