A surfactant-based wound dressing can reduce bacterial biofilms in a porcine skin explant model

Abstract

Bacterial biofilms have been found in many, if not all, chronic wounds. Their excessive extracellular matrix secretion and the metabolic changes that they undergo render them highly tolerant of many antibiotic and antimicrobial treatments. Physical removal and/or disruption are a common approach to treating wounds suspected of having bacterial biofilms. While many of these techniques use mechanical energy as the primary means of removal, we have begun to investigate if surfactants could facilitate the removal of bacterial biofilms, or if they might sensitise the biofilms to antimicrobial interventions. We tested a new surfactant-based wound gel on an ex vivo porcine skin explant model infected with a functionally tolerant 3-day biofilm. The wounds were dressed with a surfactant-based gel directly on the wound or with moistened gauze. The wounds were then wiped daily with moistened gauze, and the gel or gauze was re-applied. Each day, an explant from each group was harvested and tested for total viable bacteria counts and viable biofilm-protected bacteria counts. The results show that daily wiping with moistened gauze led to an initial decrease of bacteria, but by day 3, the biofilm had been fully re-established to the same level prior to the beginning of treatment. For the surfactant-based treatment, there was no detectable functional biofilm after the first treatment. The gauze control, which was also subjected to daily wiping, still contained functional biofilms, indicating that this result was not due to wiping alone. The total bacteria in the surfactant-treated explants steadily decreased through day 3, when there were no detectable bacteria, while the wiping-only control bacteria counts remained steady. The use of a moist gauze to wipe the visually apparent slime off of a wound appears to be insufficient to reduce biofilm over a 3-day period. Daily application of the surfactant gel dressing and wiping reduced the biofilm to undetectable levels within 3 days in a skin explant model. A 3-day regimen of dressing the wound model with a surfactant gel followed by gentle removal of the gel by wiping with a moistened gauze appears to be a simple and adequate approach to removing a bacterial biofilm infection in an ex vivo model. Additional clinical evidence is needed to determine if this promising approach can perform the same in clinically infected chronic wounds.

Keywords: Biofilm; Gel dressing; Surfactant.

© 2016 Medicalhelplines.com Inc and John Wiley & Sons Ltd.

Figures

Figure 1

The starting point for the porcine skin explant model. The wounded explant is sterilized, inoculated, and incubated for 3 days. At this point, the wound has visible biofilm on the surface. The explants are then ready for testing.

Figure 2

Wiping the visible materials away with a moistened gauze is not sufficient to remove all bacteria. The difference in total bacteria was statistically significant by Student's t‐Test (P = 0·.0003), while the difference in biofilm trended towards a difference (P = 0·07).

Figure 3

The gross experimental design. There were 3 groups: 1) only being wiped daily, but dressing with nothing more than moist gauze, 2) treated surfactant and moist gauze after wiping daily, and 3) surfactant‐SSD and moist gauze after wiping daily. Prior to application of the test agents, the prepared explants were wiped with PBS moistened gauze until the wound appeared clean. The test agents were then applied (or not for the control). The wound and test agents were covered with moistened gauze and incubated for 24 hours. One explant from each group was assayed at this point, while the rest will be re‐cleaned until visually clean with moist gauze and the test agents re‐applied.

Figure 4

For each of the 3 groups, 4 explants will be generated. At 0h, 24h, 48h, and 72h, one explant per group will be removed and assayed for total and biofilm bacteria.

Figure 5

8 samples from each explant were collected via punch biopsy. Four of the biopsies were individually sonicated in growth media and the media plated to quantify the total bacteria present. The remaining 4 biopsies were individually submerged in 50× MIC gentamicin for 24 h prior to sonication and plating to quantify viable biofilm‐protected bacteria.

Figure 6

The time courses for porcine skin explants infected with 3 day biofilms. The explants that were only wiped daily had increasing amounts of bacterial biofilm after the first day. The surfactant‐treated explants did not have any measureable biofilm after the first treatment, but did still have some planktonic bacteria up through Day 2.