Molecular basis for resistance to silver cations in Salmonella

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Abstract
Here we report the genetic and proposed molecular basis for silver resistance in pathogenic microorganisms. The silver resistance determinant from a hospital burn ward Salmonella plasmid contains nine open reading frames, arranged in three measured and divergently transcribed RNAs. The resistance determinant encodes a periplasmic silver–specific binding protein (SilE) plus apparently two parallel efflux pumps: one, a P–type ATPase (SilP); the other, a membrane potential–dependent three–polypeptide cation/proton antiporter (SilCBA). The sil determinant is governed by a two–component membrane sensor and transcriptional responder comprising silS and silR, which are co–transcribed. The availability of the sil silver–resistance determinant will be the basis for mechanistic molecular and biochemical studies as well as molecular epidemiology of silver resistance in clinical settings in which silver is used as a biocide.