23.6 Assessing the efficacy of silver containing wound dressings on silver resistant wound isolates using rapid confocal laser scanning microscopy (RCLSM)     

Steven Percival, PhD; Emma Woods, PhD; ConvaTec Wound Therapeutics GDC 

Despite evidence of silver resistance genes being documented in bacteria isolated from chronic wounds the efficacy of silver containing dressings on these isolates has not be investigated. For this study we investigated whether 4 silver resistant Enterobacter cloacae, known to contain the silE, silS and silP genes, were killed in silver containing wound dressings. Fluorescent dyes (BacLight, Live/Dead Kit) were added to fresh cultures (inoculum 108 cfu/mL) of all silver resistant wound isolates and used to visualize their viability over time using rapid confocal laser scanning microscopy (RCLSM--Leica UK). Live bacteria stained green and dead/dying bacteria turned red. When inoculated into samples of all dressings, the viability of the bacteria could be effectively monitored after 3, 24, 48, 72 hours using RCLSM. All silver resistant isolates were observed to turn progressively red (ie, died) within 24 hours; the majority of bacteria were shown to be killed in all dressings after 48 hours. In conclusion this study has shown that evidence of silver resistant genes to silver in bacteria does not necessarily translate into phenotypic resistance.