Skin’s microbiome in balance: COSSMA

A probiotic bacterium works like a tiny skincare cell-factory, making some of the skincare industry’s most hyped active ingredients, directly on the skin. Creating acids and peptides is part of the normal metabolic cell function of a probiotic cell. Which metabolites they produce, can be impacted by the type of probiotic they are, the food they have available as well as the environment that they are in.

Prebiotic for the skin

Human skin is home to billions of microbes that compose the skin microbiota. Cutaneous microbes have essential roles in the protection against invading pathogens, the education of the immune system and the breakdown of natural products. Everybody’ microbiota includes complex communities of bacteria, fungi, yeasts, mites, and viruses that inhabit the body’s surfaces.

The surface of the skin is a desiccated and nutrient-poor milieu. The cutaneous microorganisms colonise and proliferate on the skin despite its hypersaline and acid environment with low nutrient availability. Microbes adapt by feeding off available resources in sweat or sebum as well as dead cell materials. The areas of skin either fall into dry, sebaceous, or moist environments.

Bacteria dominate the skin microbiota. They predominantly belong to three phyla, Actinobacteria, Firmicutes, and Proteobacteria, with associated bacteriophages further modulating bacterial community dynamics and virulence. The most common bacterial genera are Corynebacterium, Cutibacterium and Staphylococcus. Each microenvironment on the skin will harbour its own microorganisms. While the sebaceous follicles, which create an anaerobic, lipid-rich environment, harbours the Cutibacterium and lipophilic fungi like Malassezia, the axillar area mainly consists of Gram-positive bacteria of the genera Staphylococcus, Micrococcus, Corynebacterium as well as Cutibacterium. The Staphylococcus, Cutibacterium, Micrococcus, Corynebacterium, Enhydrobacter and Streptococcus species mostly grow in the drier regions of the body.

Interestingly on average, every human hand has more than 25 phyla present on the surface. The Demodex mites are also regarded as part of the normal skin microbiota. Therefore, it will be a huge challenge to identify prebiotic compounds suited for skincare.

Consider the balance

There is a lack of knowledge about the interactions between the microbes in the microbiota – and how this is changed if specific species or strains are favoured by an added prebiotic compound to this otherwise very sparse nutrient milieu on the skin. The organisms having preference for the added prebiotic can even cause a kind of dysbiosis in the microbiota.

Lipids, acids, proteins, sebum or the like – most likely it will not be the traditional prebiotics suited for gut health that will be a good prebiotic for the skin microbiota. These dietary fibres are not expected to be good prebiotics for the common skin microbiota but can be useful in combination with the topical use of a probiotic microorganism. If the prebiotic used is known to be supportive for growth of the added probiotic strain, it will support the probiotic properties of probiotic on skin.

Dysbiosis and inflammation

Due to modern lifestyles, people have lost approximately 30% of their bacteria. Some skin diseases are associated with an altered microbial state – a dysbiosis; reversion of this dysbiosis may help prevent and/or treat the disease. Environmental stresses and other factors like use of cosmetics, disinfectants and lifestyle may cause a shift of the commensal microbes to pathogenic microbes resulting in in-flammation, itching, scaling, and other clinical signs suggesting an imbalance between skin and its microbiome.

The most common skin conditions are acne, atopic dermatitis, rosacea, psoriasis, and dandruff – all associated with changes in the microbiota. This dysbiosis is often driven by common commensal species e.g., for acne, eczema, and chronic wounds. Colonisation of skin with a pathogen is in most cases non-symptomatic, but the bacteria can cause infections when the skin’s protective barrier function is breached.

Triggering bacteria

Staphylococcus infections are often associated with atopic dermatitis, carbuncle, cellulitis, rosacea, diaper rash, impetigo, and wounds. Whether causative or a consequence, altered microbial communities can mediate tissue damage and/or inflammation across a variety of skin disorders. In the setting of atopic dermatitis, a specific clonal type of S. aureus CC1 is directly correlating with severity of disease, being associated with damage of the skin barrier, pathological inflammatory responses, and interference with adaptive immune responses.

Cutibacterium acnes is one of the skin microbiome’s most abundant resident. It is equally abundant in people with and without acne, but disease associated ribotypes occur preferentially in acne sufferers. Acnes is an example of a dysbiosis of pathogenic and non-pathogenic strains of the same species. C. acnes breaks down sebum into glycerol and free fatty acids, which trigger inflammation. Some disease associated C. acnes generate more free fatty acids than others or they can release high levels of inflammatory metabolites. That not all carriers develop acne symptoms reflects how host immunity and hormonal status govern the bacterium’s pathogenic effects. During teenage years, increased hormone levels can induce sebum production and thereby unleash symptoms. The same dysbiosis can hypothetically occur if the wrong prebiotic is being applied.

Effects of probiotics

A balanced microbiome with a high bacterial diversity is important for healthy skin. Probiotics can target underlying mechanisms in skin dysbiosis. But microbial inter-actions both with each other and with human cells vary not just by species, but also by specific strains or ribotypes within species. Even as they promote health in some settings, skin microbes can promote disease in others.

Modulating the immune system by restoring the balance in the microbiome becomes important. A direct approach to this kind of treatment involves the use of probiotics in both oral and topical form. We’re still in the pioneering phase of using topical live probiotics. But the next years will bring results with the proof of efficacy.

To be able to adjust the dysbiosis, the knowing of the ‘enemy’ causing the microbial dysfunction is important. Applying probiotics to skin is a multifactorial treatment which can be used either to adjust a dysbiosis in the skin microbiota or with the intention to apply specific metabolites produced by the probiotic bacteria.