In vivo efficacy of silver-coated fabric against Staphylococcus epidermidis

Background and aim of the study: Prosthetic valve endocarditis (PVE) is a serious complication of heart valve replacement. The use of silver-coated polyester fabric in sewing cuff fabrication is intended to reduce the incidence of PVE. In this study, three pathogenic strains of Staphylococcus epidermidis (two PVE and one peripheral vasculature pathogen) were used to evaluate infection of silver-coated and uncoated fabric. Methods: Fabric was inoculated by preincubation for 30 min in bacterial suspensions containing 10⁴, 10⁵, 10⁶, 10⁷ or 10⁸ CFU/ml, and implanted subdermally in mice for up to seven days. Bacteria adherent to fabric implanted for zero, one, three, or seven days were enumerated by sonicating the fabric and plating serial dilutions of the resulting suspension. Percent infection was assessed by implanting samples, subdermally, for seven days, then incubating explanted samples in growth media for three days and calculating the percent of fabric showing bacterial growth, for each concentration of inoculum. A logistic regression model was used to estimate curves relating percent infection to log concentration of the bacterial inoculum. These curves were used to estimate the concentration of inoculum required to produce 50% infection (ID50) for the three strains of S. epidermidis, for silver-coated and uncoated fabric. Results: Direct enumeration showed no difference in bacteria adherent to silver-coated and uncoated fabric, and no bacteria present in either fabric type in samples implanted for seven days. Nevertheless, incubation of those samples in growth media showed that many of the samples were infected. The calculated ID50 was significantly lower for silver-coated fabric than for uncoated fabric, for all three strains of S. epidermidis tested. Conclusion: Silver-coated fabric increases resistance to infection by S. epidermidis in this direct-contamination, mouse subdermal model.