Before any clinical study, substantiating a skin microbiome claim almost always starts with an in vitro screening step. Two model families are available to R&D teams: monoculture, which isolates a single bacterial strain, and co-culture, which reproduces a multi-species microbial ecosystem. The choice between the two matters: it shapes cost, timeline, and above all the ecological relevance of the results obtained. Here’s how to decide.
Monoculture models: fast screening, no interactions
Monoculture systems allow for detailed mechanistic studies of individual microbial strains. By isolating a single species, typically Staphylococcus epidermidis or Cutibacterium acnes, researchers can precisely evaluate growth kinetics, biofilm formation, and metabolite production in response to a cosmetic ingredient.
These systems offer high reproducibility and tightly controlled conditions, making them the tool of choice for quickly identifying compounds that could disrupt microbial balance. Their limitation is well known: the absence of inter-species interactions reduces the ecological relevance of the findings, since no bacterium lives in isolation on the skin. Monoculture therefore remains primarily a preliminary screening tool for raw materials or active ingredients, to check compatibility with key commensal species before going further.
One figure worth keeping in mind when scoping a study brief: up to 80% of skin bacterial species are able to form biofilms under favorable nutrient conditions, a behavior that can only be observed with full fidelity in the presence of a minimum level of microbial diversity.
Co-culture models: replicating the ecosystem, at the cost of complexity
To better replicate the natural microbial ecosystem of the skin, co-culture systems allow the simultaneous growth of multiple bacterial species in a shared environment. A notable advance in this field is the standardized TUS Skin Bacteria co-culture medium, developed by Yamamoto et al. (2024), which enables the co-culture of four key skin commensal strains: Staphylococcus epidermidis, S. capitis, Cutibacterium acnes, and Corynebacterium, reproducing the inter-species interaction and competitive colonization dynamics observed in vivo.
Co-culture models are essential for evaluating the effect of a cosmetic ingredient on overall microbial balance, biofilm formation, and metabolite exchange between species. They bridge part of the gap between the simplicity of monoculture and the complexity of the in vivo setting, revealing synergistic or antagonistic effects between represented strains that are invisible in a single-species system.
Another useful data point to support the case for this model: multi-species communities show 2 to 3 times higher resistance to ingredient-induced disruption compared to monocultures. In other words, an ingredient flagged as “disruptive” in monoculture may prove far better tolerated in a multi-species context, and vice versa, which has direct consequences for how a screening result should be interpreted.
How to choose between the two models based on your study objective
The table below summarizes the selection criteria depending on the stage of product development and the type of claim targeted.
| Criterion | Monoculture | Co-culture (e.g. TUS Skin Bacteria) |
|---|---|---|
| Main objective | Fast screening of raw materials | Evaluation of overall microbial balance |
| Strains studied | A single isolated species | Several strains simultaneously (e.g. 4 key strains) |
| Ecological relevance | Limited, no inter-species interactions | Higher, competitive dynamics reproduced |
| Reproducibility | Very high | High, but more sensitive to culture conditions |
| Cost and timeline | Low, fast | Higher, more complex protocol |
| Recommended use | Pre-selection of actives, compatibility with a target strain | Microbial balance claims, synergistic/antagonistic effects |
In practice, the two approaches are often complementary rather than competing: monoculture serves as a first filter to rule out ingredients clearly incompatible with major commensal strains, before a narrower set of candidates is tested in co-culture to validate an effect on the ecosystem as a whole. For a claim intended for marketing use, only co-culture, or a 3D or ex vivo model as a complement, can genuinely support a message around microbial “balance” or “diversity.”
To identify laboratories offering either of these models, the Skinobs platform references providers specialized in microbiome screening, both monoculture and co-culture.
Discover skin microbiome testing solutions on Skinobs → https://www.skinobs.com/
