Laboratory Research
The intact skin model was established using S. epidermidis to form a 3-day old biofilm. Sterile, intact skin explants were inoculated using gauze saturated with early log phase bacteria at a concentration of 105 CFU/mL applied evenly across the epidermis for 2.5 h followed by removal of the gauze and incubation at 37oC on soft agar (0.5% agar) for 3 days. The presence of biofilm was confirmed by microscopy and treatment of explants 3 days after inoculation with a dilute solution of hypochlorous acid to remove planktonic bacteria. Various commercial and experimental products were assessed for biofilm removal.
Results:
Histological analysis of the tissue revealed densely packed S. epidermidis on the epidermis as well as within the hair follicles. Explants with a 72 h biofilm were treated topically for 24 h with varying results. Commercial hypochlorous acid treatments exhibited a 1 log reduction in total bacteria, while povidone iodine (50% in PBS) and gentamicin treatment (3 mg/mL) both showed a 1.5 log reduction in bacteria relative to controls (significant at p <u>< 0.05), and an experimental formulation containing a biofilm disrupter and a mixture of all-natural fatty acid esters showed >5 log reduction relative to controls significant at p <u>< 0.05).
Discussion:
This study describes a reproducible method for establishing a mature S. epidermidis biofilm on porcine skin explants with intact epidermis and dermis. A robust biofilm was observed on the explants in 72 h with an average loading of 7-8 logs per explant. Treatments showed varying degrees of efficacy against the biofilm, with an experimental fatty acid ester formulation showing the best results of >5 log reduction relative to controls. These significant results demonstrate the utility of this ex vivo model of biofilm and the promising efficacy of an experimental fatty acid ester formulation relative to commercial formulations of povidone iodide, hypochlorous acid and antibiotics.