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

Abstract

Electrochemical techniques were used to study the behavior of Escherichia coli on the addition of <or=10 microM AgNO(3). 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 microM AgNO(3), as determined by the time until respiration ceased, increased in the absence of glucose and in the presence of K(+). The uptake of 1 microM Ag(+), measured from the stripping peak height of Ag electrodeposited on a 25 microm 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 microM 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.