Assessment of antibacterial activity of silver ions in infected diabetic foot ulcers - an answer to antibiotic resistance

Background: Easy accessibility and irrational use of antibiotics has led to emergence and spread of multidrug bacteria in nosocomial and community settings. MDR strains of Pseudomonas aeruginosa, Staphylococcus aureus and Enterobacteriaceae are commonly isolated from infected diabetic ulcers. Escalating antibiotic resistance has led us to reconsider use of heavy metals particularly silver which is known to reduce bacterial burden in infected wounds. This study aims to assess the bactericidal and clinical effect of silver alginate foam dressings on infected diabetic foot ulcers. Methods & Materials: Fifty cases of infected diabetic foot ulcers were studied. Quantitative bacterial cultures on sheep blood agar were performed as baseline (prior to treatment) and at 7 and 14 days following treatment with silver alginate dressing. Results of quantitative cultures were co-related with clinical improvement in ulcer size and local signs of infection. Bacteria isolated were identified and antibiogram was determined as per CLSI guidelines. Killing curves were recorded by inoculating the surface of silver alginate dressing with 105 bacteria. Sensitivity and duration of silver ion activity was assessed by disc diffusion method on nutrient agar using 7mm disc of silver dressing. Growth inhibition zone diameters were recorded by serial transfer of silver ion foam disc onto freshly inoculated plates for 7 consecutive days. Results: Bacteria isolated included S.aureus 32% (28% MRSA), E.coli 24% (39% ESBL producers, 12% MBL producers), P.aeruginosa 37% (15% MBL producers), Enterobacter spp 4% and Citrobacter 3%. Killing curves showed sterility approximately one to 2.5 hours following exposure to silver ions. All the isolates were sensitive to silver ions irrespective of their antibiotic resistance status. Growth inhibition zone diameters were maintained steady upto 7 days. In all cases decrease in bacterial load was associated with decrease in ulcer size. Conclusion: This study shows topical use of silver ions could serve as an effective alternative to topical or oral antibiotics in management of infected wounds. When used once weekly silver alginate foam dressing appears to be effective in reducing wound bio-burden which is positively associated with ulcer healing. Thus we can conclude that silver ions can be used effectively for treatment of chronic ulcers.