Interest in skin flora is increasing every year. In this decade many reports showed relationships between skin diseases and skin flora. For example, Staphylococcus aureus and some strains in Cutibacterium acnes are related to atopic dermatitis and acne vulgaris, respectively. This is why they are thought to be non-beneficial skin bacteria or pathogens. On the other hand, there is little knowledge about relationships between healthy human skin conditions and skin flora or beneficial skin bacteria. Staphylococcus epidermidis, the best-known beneficial skin bacteria, release lipases that are effective for degrading excessive sebum and producing glycerol and free fatty acids. These decomposition products are thought to be effective for skin moisturizing and controlling skin pH.¹ However, there were no other well-known beneficial skin bacteria related to healthy skin.

Recent studies found some strains of Coagulase-negative staphylococci (CoNS; also including S. epidermidis) produce specific antimicrobial peptides against S. aureus or C. acnes,^2,3 making them good beneficial skin bacteria candidates. In order to find out other beneficial properties of CoNS, we evaluated their lipase activity that is the beneficial property of S. epidermidis. Using a lipase activity indicator, we revealed that S. capitis and S. hominis, the major Staphylococci in human skin, have higher lipase activity than S. epidermidis. Based on these data, we redefined CoNS as beneficial skin bacteria.
Unfortunately, our analysis showed that facial CoNS decreased with aging (Fig. 1). This probably causes many aging features, including moisture loss. Accordingly, we thought that growing CoNS using a prebiotic mechanism would improve skin condition.

The Benefits of Lactobacillus K-1
We searched many candidates for skin prebiotic ingredients, and focused on the heat-killed lactic acid bacteria, Lactobacillus K-1. Lactobacillus K-1 (Lactobacillus casei subsp. casei 327) was originally developed by Kameda Seika Co., Ltd, a Japanese rice cracker manufacturing company,⁴ which worked on a project that investigated the potential of plant origin lactic acid bacteria, and finally arrived at this lactic acid bacteria strain. Plant-derived lactic acid bacteria play very important roles in Japanese traditional fermented foods such as miso, pickles and tea. Lactobacillus K-1 was selected from hundreds of lactic acid bacteria strains. Interestingly, Kameda Seika reported that ingested Lactobacillus K-1 improved not the only function of the intestine but transepidermal water loss,⁵ too.

We developed novel cosmetic ingredient Fairy Flora K-1 (INCI: Lactobacillus, Maltodextrin) from this food ingredient Lactobacillus K-1. This heat-killed lactic acid bacteria has no risk of contamination in both factories and cosmetic containers. Although it is precipitated in low viscosity solvents, it is suitable for use in gels or creams, or in combination with a viscous agent. Here, we evaluated the effect of Fairy Flora K-1 on the growth of CoNS to maintain skin condition.

We established an in vitro assay system for evaluating the effect of Fairy Flora K-1 on the growth of CoNS. In this assay system, Fairy Flora K-1 showed growth-promoting activity for not only S. epidermidis (Fig. 2) but also S. capitis. In order to examine this effect in vivo, we designed a placebo-controlled human trial using a facial gel containing 0.1% Fairy Flora K-1. The human subjects used this gel twice a day for four weeks. We compared skin flora, skin moisture content and skin pH between before and after the test period. Skin flora analyses were performed by using NGS (Next Generation Sequencer) and then the rate of CoNS was calculated. The placebo group showed a small difference in the rate of CoNS from the initial value, on the other hand, many of the K-1 group increased the rate of CoNS (Fig. 3A). The skin moisture content decreased in the placebo group because this trial was performed in early winter, a season when the atmosphere gets dry. Yet, Fairy Flora K-1 increased moisture content even if in such a dry condition (Fig. 3B). Finally, we evaluated skin pH. High skin pH correlates with skin dryness. Fairy Flora K-1 significantly improved skin pH in subjects whose initial pH was above 6.0. Glycerol and free fatty acid production by CoNS contributed to these results.

Improving the Barrier
Additionally, we evaluated the effect of Fairy Flora K-1 on normal human epidermal keratinocyte. Addition of 0.1% Fairy Flora K-1 increased the mRNA expression of an endogenous antimicrobial peptide, β-defensin 3. Such antimicrobial peptide is known to be effective for reducing pathogens such as S. aureus, but not CoNS. Fairy Flora K-1 also increased stratum corneum formation factors, filaggrin and involucrin (Fig. 4). These factors are important for forming a barrier to hold water in the epidermis and are known to reduce certain diseased conditions such as atopic dermatitis. These data mean Fairy Flora K-1 improves two types of endogenous skin barrier functions, anti-pathogenic and moisturizing barrier. In human monitor trial data, these properties are thought to contribute to improving skin flora and skin moisture.

There are unknown relationships between healthy skin and skin flora, yet, the subject is getting more attention in the cosmetic field, too. In our investigation, Fairy Flora K-1 increased the beneficial skin bacteria CoNS that declines with aging. Increasing CoNS improves skin moisture content and weak acidic condition. Moreover, Fairy Flora K-1 reinforced two important barriers against water loss and pathogen in epidermal keratinocyte. The recent prevalence of COVID-19 forced us to reexamine the immune system’s importance. Lactic acid bacteria are commensal bacteria that are well-known to maintain the intestinal immune system. Although effects of Fairy Flora K-1 on the skin were not proven to be due to immune activation, the increased expression of antimicrobial peptide β-defensin 3 by Fairy Flora K-1 strongly suggests the involvement of innate immune system. Today the relationship between bacteria, viruses and skin care must be examined. Fairy Flora K-1 is a novel ingredient that improves skin’s barrier function. 

Ichimaru Pharcos, +81-58-320-1032, www.ichimaru.co.jp

References:

1. Scheimann LG, Knox G, Sher D, Rothman S. The role of bacteria in the formation of free fatty acids on the human skin surface. J Invest Dermatol. 1960;34(2):171-174. doi:10.1038/jid.1960.23
2. Williams MR, Costa SK, Zaramela LS, et al. Quorum sensing between bacterial species on the skin protects against epidermal injury in atopic dermatitis. Sci Transl Med. 2019;11(490). doi:10.1126/scitranslmed.aat8329
3. O’Neill AM, Nakatsuji T, Hayachi A, et al. Identification of a Human Skin Commensal Bacterium that Selectively Kills Cutibacterium acnes. J Invest Dermatol. Published online 2020. doi:10.1016/j.jid.2019.12.026
4. Saito Y, Mihara T, Oki M, Kumagai T. Effects of heat-killed Lactobacillus casei subsp. casei 327 Intake on Defecation in Healthy Volunteers : a Randomized, double-blind, placebo-controlled, parallel-group study. Biosci Microbiota, Food Heal. 2018;37(3):59-65.
5. Saito Y, Mihara T, Maruyama K, et al. Effects of intake of Lactobacillus casei subsp. casei 327 on skin conditions: A randomized, double-blind, placebo-controlled, parallel-group study in women. Biosci Microbiota, Food Heal. 2017;36(3):111-120. doi:10.12938/bmfh.16-031