Silver dressings are used to manage
wounds at risk of
infection or locally infected. This in vitro study was conducted to assess the prevalence of
silver resistance genes in 112 bacterial isolates obtained from the
diabetic foot ulcers of patients attending the
Diabetic Foot Clinic at Tameside General Hospital, UK. Using polymerase chain reaction to screen for three
silver-resistance transcriptional units--silE, silS and silP--two
silver-resistant bacteria were identified; both are strains of Enterobacter cloacae, an organism rarely implicated as a primary pathogen in chronic
wounds. No recognized
wound pathogens (Staphylococcus aureus-24 isolates and Pseudomonas aeruginosa-nine isolates) were found to contain
silver-resistant genes. Analysis of the efficacy of
silver-containing dressings on the
silver-resistant strains of Enterobacter cloacae using confocal
laser microscopy showed that, despite evidence of genetic resistance to
silver, all strains were killed following a maximum of 48 hours of exposure to the dressings. Results suggest that presence of
silver resistance genes is rare and that genetic resistance does not necessarily translate to phenotypic resistance to
silver. While
silver resistance in
wound care should be monitored, the threat of widespread resistance is low and
silver-containing dressings remain an extremely important tool in managing
wound infection.