Prevalence of Phenotypic Silver Resistance in Clinical Isolates
Clinical awareness of bacterial silver resistance has increased in the last decade due to the widespread use of silver in medical treatments. Although there continues to be a lack of evidence supporting the development of silver resistance, it remains a topic of concern in wound clinics. In addition, scientific interest in silver resistance has increased due to the potential of cross resistance. Silver-resistant genes are encoded by the same plasmid that encodes traditional antibiotic resistance. Although there are clear molecular basis for silver resistance, phenotypic expression has yet to be observed.
The authors' results failed to demonstrate any evidence of emerging clinical significance supporting silver's inability to kill bacteria. All 130 strains tested showed no growth when exposed to the silver dressing, including the multidrug-resistant bacteria. These findings support previous work showing a lack of silver resistance in clinical isolates. An in vitro study showed silver alginate dressings inhibited the growth of 115 clinical samples. In addition, this study showed Enterobacter cloacae to have the highest silver tolerance. This finding is particularly interesting because bacteria strains containing silver-resistant genes identified in previous studies were those of the Enterobacter cloacae species. Increases in silver tolerance in this species could potentially be initial observation of mild phenotypic expression. Further testing is needed before conclusions could be made.
Discussion
Clinical awareness of bacterial silver resistance has increased in the last decade due to the widespread use of silver in medical treatments. Although there continues to be a lack of evidence supporting the development of silver resistance, it remains a topic of concern in wound clinics. In addition, scientific interest in silver resistance has increased due to the potential of cross resistance. Silver-resistant genes are encoded by the same plasmid that encodes traditional antibiotic resistance. Although there are clear molecular basis for silver resistance, phenotypic expression has yet to be observed.
The authors' results failed to demonstrate any evidence of emerging clinical significance supporting silver's inability to kill bacteria. All 130 strains tested showed no growth when exposed to the silver dressing, including the multidrug-resistant bacteria. These findings support previous work showing a lack of silver resistance in clinical isolates. An in vitro study showed silver alginate dressings inhibited the growth of 115 clinical samples. In addition, this study showed Enterobacter cloacae to have the highest silver tolerance. This finding is particularly interesting because bacteria strains containing silver-resistant genes identified in previous studies were those of the Enterobacter cloacae species. Increases in silver tolerance in this species could potentially be initial observation of mild phenotypic expression. Further testing is needed before conclusions could be made.
SHARE
