Reduction of Multi-Drug Resistant Pathogens and Associated Virulence Factors in a Burn Wound Infection Model: Further Understanding of the Effectiveness of a Hydroconductive Dressing

Introduction
Virulence factors produced by pathogens can impede wound healing by creating a more invasive infection and altering the host’s immune response. Methicillinresistant Staphylococcus aureus (MRSA) produces virulence factors that have been found to induce shock, sepsis, and enhance bacterial survival. A unique hydroconductive dressing has been designed to move large amounts of exudate, slough, necrotic tissue, bacteria, and other wound debris from the wound to the dressing. In pilot work, this experimental dressing was observed to reduce both bacteria and virulence factor levels in MRSA-infected burn wounds. The present experiments were designed to further evaluate the efficacy of Drawtex® (experimental dressing) as compared to a standard of care (control dressing) in an in vivo model of burn wound infection.

Methods
To characterize the in vivo impact of this dressing on infection and healing, an infected burn wound model in Sprague-Dawley rats was used (see above). MRSA and virulence factors (TSST-1 and PVL) were quantified using quantitative cultures and ELISA respectively. Laser Doppler imaging (LDI) was used to examine wound perfusion. Local immune response was assessed by quantifying mRNA expression of genes involved in innate immunity using gene-specific primers in real time RT-PCR.

Results
By day 3, less (n=6, p<0.05) MRSA was measured in wounds treated with experimental-dressing (5 x 109 CFU/g) compared to control-dressing wounds (2.3 x 1012 CFU/g). Quantities remained lower in the experimental group on day 6 (p<0.001) and were further reduced on days 9 (1.5 x 106 CFU/g, p<0.001) and 14 (Fig. 1). More MRSA was quantified in the experimental dressing than in control dressing at all time points (p<0.05), increasing through day 9. Experimental dressing-treated wounds contained less TSST-1 and PVL than controls (p<0.01) on days 6, 9, and 14, while conversely, the experimental dressing itself contained more TSST-1 and PVL by day 6 than the control dressing (p<0.001; Fig. 2). Induction of TLR2, NLRP3, and IL6 was significantly lower in experimental-dressing treated wounds than in controls on days 6 and 9 (p<0.05; Fig.3). An increase in perfusion was seen in the experimental wounds after day 3 (Fig. 4).

Conclusion
In summary, the hydroconductive dressing provided a significant reduction in pathogen and virulence factors—exceeding that of a control dressing. Further, as a result of clearance of virulence factors from the wound bed, a requisite reduction in host innate immune response was observed.