Identification and Characterization of Silver Tolerant Bactria in Venous Leg Ulcers

Venous leg ulcers (VLU) are a significant burden on the healthcare system and patients. Silver based therapies are common practice yet recently reports emerge of silver resistant bacteria in VLU. We designed an exploratory, single center, observer masked, active control, randomized trial to investigate the effectiveness of Dialkylcarbomoyl chloride dressing (Cutimed® Sorbact®) in modifying bacterial load in VLU. Herein we report preliminary, blinded analysis of silver tolerance in our cohort. Nine subjects with VLU were randomized to receive Dialkylcarbomoyl chloride or silver (Acticoat®) dressings in addition to standard care consisting of sharp debridement and 4-layer compression system. All patients received silver-based therapy in the weeks leading up to randomization. Wound tissue was collected at baseline, 2 and 3 weeks into treatment and plated on silver agar. Quantification of bacterial load was performed using Real-Time PCR amplification of 16S rRNA gene. After initial growth on nutrient rich media all isolates were tested for growth on Luria Broth agar supplemented with 250 _M Ag+ using patch method. Bacterial colonies able to grow on silver agar were identified based on 16S rDNA gene sequence. All wounds demonstrated high levels of silver tolerant bacteria, both aerobic and anaerobic as well as gram positive and negative species. At baseline, 9 of the 9 subjects demonstrated aerobic and 8 out of 9 subjects demonstrated ≥70% anaerobic silver tolerant colonies. The most common silver tolerant species identified were Staphylococcus, Escherichia coli, Pseudomonas aeruginosa, Corynebacterium sp and Morganella sp. Silver tolerance in VLU may be more widespread than previously thought. Identification of silver resistance genes and correlation with healing outcomes are ongoing.