SKIN MICROBIOME
changes. While it may seem like an enormous challenge to create personal care products to support the skin microbiome owing to this variation, a few assumptions are made about the microbiota likely to be present and some general tactics can be deployed with the aim of promoting microbiome ‘health’.
Targeting the microbiome: probiotics, prebiotics and postbiotics So, what kind of products do we expect to target the skin microbiome? The topical application of products intended to affect the skin microbiome have the potential to do so in several direct and indirect ways. Below we describe five common approaches: ■ The removal or killing of either a specific species of microorganism or an entire mixed species population. This approach may be the most advantageous in certain skin conditions whereby it is suspected that there is a predominant microorganism resulting in pathogenesis. This approach not only focusses on the screening of the active, but also the assessment of surfactants which can impact resident microorganisms. ■ The addition of live microorganisms, ‘Probiotics’ or ‘good bacteria’ to an existing flora. The aim of this would be to change the microbial profile of the skin to what is considered to be a more beneficial microbiome. ■ The supplementation of the existing microbiome with nutrients or ‘Prebiotics’ in the aim of promoting overall microbial development or encouraging a particular species of microorganism to thrive. You can think of pre- biotics as food for the ‘good bacteria’. ■ The supplementation of the existing microbiome with microbial by-products. The term for this is coined as ‘Postbiotics’ and is a relatively new term with the focus being on creating an environment that is representative of the end point of a healthy state. Postbiotics are non-viable bacterial products (E.g., cell- wall components) or metabolites released by beneficial bacteria, such as vitamins and lactic acid. In other words, they come from the fermentation (breakdown) of bacteria. In practice, they are created from cultures of probiotics that selectively influence the microbiome for healthier outcomes. Therefore, many microbial ferment lysates and extracts present in probiotic cosmetics can be thought of as postbiotics.5 ■ Targeting the environmental factors of the microbiome such as pH, moisture and oiliness of skin, which in many ways, can dictate the types of microorganisms that can inhabit these sites. In recent years skin care brands have
emerged entirely focussed on products to promote and support the skin microbiome. The vast majority of these claim to contain probiotics, however, many contain inactivated, rather than living, microbes. Probiotics in cosmetic products can present certain challenges concerning the safety and stability of the products given the presence of live microorganisms. Cosmetic products must not cause us harm and need to survive long enough to sit on the shelves and in our cupboards. Similarly, there are no standard test
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60 Figure 2: S. aureus attachment to keratinocytes.
methods to substantiate claims for probiotic- based products and the effects on the skin microbiome. If this trend is to stay consumers will need, want and deserve proof of the efficacy and safety of their chosen regime. It follows then that few health claims have actually been authorised by regulatory bodies for the use of these supplements in skin care. To address this, we clearly need a suitable model for the skin microbiome on which to test.
Modelling the skin microbiome, or is that a ‘biofilm’? Establishing that the skin microbiome differs between individuals presents the biggest challenge in creating robust and reproducible testing. Moving forward, we need to be confident that we can create and adjust conditions that accurately mimic a range of microbial profiles so that the results are valid for the general population. The colonisation of bacteria on the skin (to represent ‘real- world’ conditions) depends on the successful attachment and replication of these microorganisms. When one considers the microbiome there
are obvious parallels with ‘biofilms’. A biofilm is defined as a community of microorganisms that attach to a surface or each other and encase themselves in an exopolysaccharide matrix. Perfectus Biomed’s considerable experience in the area of biofilms afforded us the skills and knowledge around microbial attachment and inter-microbial interactions which we have successfully applied to model the skin microbiome. The UKAS accredited biofilm test methods employed by Perfectus Biomed allow us to study microbial communities (single and multi-species) both on abiotic surfaces, such as plastic and metal. We have also developed complex multi-species biofilm models in-house for customised testing and designed biofilm models on ex vivo porcine and human skin. The studies on abiotic surfaces are often used to test biocides and disinfectants, anti-biofilm coatings for medical devices and implants, and anti-biofilm wound care products. In the realm
of cosmetics and personal care the assessment of product efficacy on colonised hard surface models can provide much needed preliminary data before moving on to more complex, ‘real- world’ scenarios. However, these models do not mimic the biological impact of host cells on bacterial colonisation, in other words, live human skin. Work was done to build upon the existing models using our experience in cell and microbiology to address three key challenges. Each model more complex and closer to ‘real skin’ than the previous.
1: Assessing bacterial interaction with live cells To address this first challenge we designed a reproducible, high throughput in vitro bacterial attachment assay. We selected human primary neonatal keratinocytes to mimic the epidermis of the skin. We then selected a microorganism, in this case, Staphylococcus aureus, as a well-known, skin relevant microorganism. We then assessed the attachment of these microorganisms to the keratinocytes in both a time and dose-dependent manner. The output of this assay was the microbiological quantification of attached bacteria to human cells.
The results of this study showed positive
S. aureus attachment between the contact times of 30 and 180 minutes. The degree of bacterial attachment to cells increased as the contact time increased, demonstrating a time- dependent response. In addition, there was an increased level of bacterial attachment to cells as the concentration of bacteria increased, indicating a dose-dependent response. These were all patterns in data that we expected and we were very pleased with the reproducibility of the assay. Finally, the biggest challenge to overcome when introducing bacteria to in vitro cell culture, is the compromise of cell viability. In this study, we noted that cell viability was not impacted and therefore presented a great opportunity for downstream analysis of host cell response to bacterial attachments, such as inflammation and collagen production.
January 2021 PERSONAL CARE 120 Time (minutes) 240 7 CFU mL-1■ 1x10∧ 6 CFU mL-1■
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