Targeting S. aureus biofilm formation to reduce the occurrence and the severity of flares-up in children with atopic dermatitis

Atopic dermatitis (AD) is an inflammatory chronic dermatosis characterized by a marked dysbiosis with a decline of biodiversity. During AD flare-ups, S. aureus biofilm-growing was described as the major colonizer in the skin lesions and its production strength was recently correlated with the disease severity (Di Domenico et al. Sci Rep 2018; Di Domenico et al. Microorganisms 2019). This suggests that the biofilm production by S. aureus plays a major role in the chronicity and severity of AD. Therefore, the aim of this study was to evaluate the prevention of S. aureus biofilm formation of both the patented active agent, called Skin Barrier Therapy (SBT) and a dermo-cosmetic balm (containing SBT), that was demonstrated as reducing the occurrence of relapses and the severity of AD in children.

In microplates, bacterial suspensions of S. aureus strain (CIP 4.83) (10⁶ CFU/mL) were mixed and incubated at 37 °C for 4 hours with SBT (from 0.1 to 5x10^-5%) or for 4 or 6 hours with the balm (500 mg/mL). For SBT, the prevention of S. aureus biofilm-growing was evaluated by the BioFilm Ring test. The principle is based on the capacity of bacteria to immobilize paramagnetic microbeads when forming a biofilm at the surface. After magnet contact, free microbeads are concentrated in the center of the wells’ bottom, forming a black ring, whereas those blocked by sessile cells remain in place. In microplates, magnetic microbeads (TON004) were added (10μL/mL) to the bacterial suspensions incubated with SBT at 37°C for 4 hours. After adding a contrast liquid, the microplate was magnetized for 1 min on the block-test to reveal the mobility of the microbeads. Image acquisition and analysis of the microplate was performed using BFC Elements 3.0 software. For the balm, to recover the biofilm phase, the microplate was sonicated after addition of PBS to each well. The "biofilm" supernatants were then diluted and counted after filtration (0.2μm) on membranes. The agar plates were incubated at 37°C for 24 hours and then counted.

The SBT presented an inhibitory activity of 92.0% at 8x10^-4 on the proliferation of S. aureus in a biofilm form after 4 hours. In presence of the dermo-cosmetic products, the S. aureus proliferation as a biofilm was reduced for the balm by 3 log at both 4 and 6 hours compared to the controls, corresponding to a reduction of -99.9% for both. These effects were not due to bacterial toxicity of the product because no difference of the proliferation was observed between 4 and 6 hours.