Assessment of Microbial Transfer Efficiency and Antimicrobial Efficacy for a Silver Embedded Antimicrobial Coating

Abstract

Hospital acquired infections (HAIs) are becoming an issue of increasing importance within the medical field. A recent report from the United States Centers for Disease Control and Prevention (CDC) states that over 700,000 HAIs occurred during 2011, with approximately 75,000 deaths attributed or associated with these infections (CDC, 2016). Historically, inadequate disinfection has been implicated in HAI outbreaks (Reiss et al. 2000). This has stimulated a demand for passive disinfection methods that eliminate the need for frequent human intervention to reduce microbial levels on surfaces. This study examined the antimicrobial efficacy and transfer capabilities for a silver embedded slow release coating. The coating was designed to be used on high touch surfaces where at-risk hospital patients may likely be exposed to pathogens. The efficacy and transfer of two types of bacteria and a one virus were studied using a silver embedded coating and compared to non-coated stainless steel slides. Enterobacter aerogenes (ATCC 13048), Staphylococcus aureus (ATTC 6538P), and MS2 15597 B-1 bacteriophage were the study organisms. An inoculum was placed onto each carrier. The carriers were either harvested directly (i.e. controls), or subjected to finger-touch transfers after 0, 1, 4, or 8 hours after drying. The maximum observed reduction due to the antimicrobial properties of the coating for E. aerogenes was 4.49 log10, compared to 1.65 log10 for the non-coated carrier controls. The average transfer efficiencies of E. aerogenes to finger pads for both carrier types was 10%. The maximum reduction of S. aureus was 1.59 log10 for the silver-coated carriers, relative to 1.49 log10 for non-coated controls. For S. aureus, the average transfer efficiencies were 13% and 36% for silver-coated and non-coated respectively, with no statistical significance observed (p=0.10). MS2 bacteriophage levels were not significantly reduced; however, the mean transfer efficiency to the finger pads from the non-coated control carriers was slightly greater at 10%, compared to only 6% for the silver-embedded carrier The efficacy and transfer efficiency values obtained were utilized to conduct a Quantitative Microbial Risk Assessment (QMRA) for both Staphylococcus aureus and Enterobacter aerogenes. Klebsiella pneumoniae was chosen as the representative model organism for E. aerogenes in the study. For the given exposure assessment scenario and parameters, the infection risk for K. pneumoniae following transfer of the organism to finger pads from non-treated stainless steel control carriers was 3 orders of magnitude greater than that following finger pad contamination from silver embedded carriers. Methicillin-resistant Staphylococcus aureus (MRSA) was chosen as a representative for Staphylococcus aureus (ATTC 6538p). For this risk scenario, the coated vs non-coated surface was the determining factor that made the risk of infection of MRSA acceptable vs not acceptable for a week long hospital stay.