Evaluation of Enhanced Skin Probiotics in Organotypic Skin Models

The skin is the largest organ in the human body and serves as the main barrier separating the body from our surroundings. Simultaneously, the skin surface is home to a myriad of microorganisms that play a key role in health. Although many descriptive studies have mapped the skin microbiota composition, novel approaches are needed to elucidate the casual relations among these microbes and the skin. We engineered Cutibacterium acnes, the most abundant skin commensal, for its establishment as a synthetic biology chassis to develop tools towards understanding these relations and enable innovative microbiome-based therapeutics. Our C. acnes strain harbouring our modular replicative plasmid was tested for survival, applicability and safety in 3D organotypic human epidermal equivalent (HEE) models. The results demonstrated that our strain was able to replicate on the model surface without causing any major inflammatory response. Furthermore, our strain successfully expressed heterologous fluorescent reporters, enabling its imaging in tissue samples. We additionally studied the in vitro response of C. acnes to stresses such as temperature shock or oxidative stress. By adapting its natural promoters, we developed biosensors capable of a 2.5-fold induction in response to temperature increase or oxidative drugs. Moving forward, we plan to use HEE models with cytokine cocktails to emulate inflammatory conditions and evaluate the capacity of these biosensors to detect diseases biomarkers. In conclusion, we showed that our engineered C. acnes is a versatile platform and, together with the HEE model, we have enabled a design-build-test workflow for the development of enhanced skin probiotics.