New technologies make it possible to identify microorganisms belonging to a much larger number of species and to estimate their number in a given sample. Today we know that microorganisms colonize the guts, the sexual organs, the skin and even some solid tumors.
Microorganisms in the gut extend the digestive capabilities of the individual, prime the immune system, produce vitamins, degrade xeno-biotics and help resist pathogen colonization.1,2 The study of non-obese and obese individuals showed that there are two major types of bacterial populations colonizing the guts, Low Bacterial Richness and High Bacterial Richness. Individuals with Low Bacterial Richness are characterized by more marked adiposity, insulin resistance and dyslipidaemia when compared with High Bacterial Richness individuals. Obese individuals in the Lower Bacterial Richness group also gain more weight over time.3
Reversing obesity seems to be within reach. Gut microbes contribute to body weight regulation by influencing metabolic functions. The gut microbiome can improve the ability of the individual to extract and store energy from the diet, thus helping body weight gain, but some microbes exert opposite, beneficial effects, thus potentially leading to reducing weight increase and even to weight loss. An obese-associated microbiome was extracted from one individual, a culture of Christensenella minuta added and transplanted in the gut of other mice. The transplanted, modified microbiome reduced weight gain and altered the microbiome of recipient mice.4 Microbiomes can also be changed by appropriate diets in human individuals. For instance, diets composed entirely of animal or plant products affect differently the composition of the microbiome. This is of great importance since the animal-based diet appears potentially obesogenic by decreasing the levels of Firmicutes, a microorganism involved in the production of the antiobesogenic butyrate.5
An Impact on HIV
It has been reported (Science, vol 353 p. 331 July 22, 2016) that women with an abundance of Prevotella bivia and Gardnerella vaginalis in their vaginal microbiome are 13 times more at risk of becoming infected with HIV than those with scant amounts of P. bivia and G. vaginalis. Topically applying the antiviral drug tenofovir in women with more than 50% Lactobacillus in their vaginal flora is nearly four times more effective in preventing HIV infection than in women with less than 50% Lactobacillus in their vaginal microbiome. It turns out that Gardnerella vaginalis degrades tenofovir and grows well in the absence of Lactobacillus.
Keeping on topic, the skin microbiome is different when a baby is born vaginally or via a Cesarean cut, and is modified during one’s lifetime by the environment and lifestyle. To belong to the cutaneous microbiome, a microorganism must adhere, multiply and invade. Proteases and other enzymes are secreted to carve a niche, while biofilms are synthesized to favor adhesion. Surface biochemistry and cutaneous microflora find a balance that can be perturbed.6,7 As a matter of fact, the molecular composition of skin is defined not only by skin cells and microbes but also by daily routines, including the application of hygiene products.
Among the best-known microorganisms in the skin microbiome is the infamous Corynebacterium. Niched in the axillary pits, it digests lipids and releases volatile, malodorant molecules. Propionibacterium acnes, a pro-inflammatory anaerobic organism, is associated with acne on the face and with dandruff in the scalp. The scalp is also the niche for the fungus Malassezia furfur and the bacterium Staphylococcus.
Other Skin Diseases
Atopic dermatitis might be the consequence of a modified skin microbiome. A small study with facial swabs pointed out that Stenotrophomonas maltophilia was significantly more common in the 13 atopic dermatitis patients tested whereas Dietzia maris was significantly more common in the 10 healthy controls.8
In another study, Bifidobacterium animalis subsp lactis or placebo was administered by general route to 44 AD patients. Pruritus was alleviated in patients receiving probiotic treatment. The anti-pruritus, anti-nociceptive metabolite Kynurenic acid was found in patients with decreased pruritus.9 These results are confirmed by several other studies and ongoing projects. Patients receiving probiotic treatment via the general route showed a significant improvement in clinical parameters from baseline. Topical treatments are effective, too! A topical cream containing a lysate of Bifidobacterium longum sp or a placebo was applied twice a day for two months on volunteers with reactive skin. The volunteers who applied the cream with bacterial extract had a significant decrease in skin sensitivity.10
And what about cosmetics? It is possible to analyze the composition of the skin microbiome and to study the role of its components at the onset of undesirable skin conditions. Microorganisms can provoke a range of maladies, including pruritus, sensitivity, inflammation, rosacea, malodor, dryness, acne and dandruff. It should be possible to topically apply specific nutrients that favor the growth of beneficial microorganisms so that the harmful ones are outgrown and eliminated.
And to fulfill the dream of “beauty from within,” it should also be possible to ingest specific prebiotics in order to associate topical and general “treatments” to improve skin conditions without falling into the “drug” category. That will constitute a major challenge for the US FDA—if regulators continue to insist that cosmetic companies can only sell snake oil!
- Bohnhoff M et al (1954) Effect of streptomycin on susceptibility of intestinal tract to experimental Salmonella infection. Proc Soc Exp Biol Med 86 : 132-137
- Patterson E et al (2014) Gut microbiota, the pharmacobiotics they produce and host health. Proc Nutr Soc 73 : 477-489
- Le Chatelier et al (2013) Richness of human gut microbiome correlates with metabolic markers. Nature 500 : 541-546
- Goodrich JK et al (2014) Human genetics shape the gut microbiome. Cell 159 : 789-799
- David LA et al (2014) Diet rapidly and reproducibly alters the human gut microbiome. Nature 505 : 559-563
- Grice EA et al (2008) A diversity profile of the human skin microbiota. Genome Res 18 :1043-1050
- Nakatsuji T et al (2013) The microbiome extends to subepidermal compartments of normal skin. Nat Commun. 4 : 1431-1442
- Dekio I et al (2007) Characterization of skin microbiota in patients with atopic dermatitis and in normal subjects using 16S rRNA gene-based comprehensive analysis. J Med Microbiol 56 : 1675-1683
- Matsumoto M et al (2014) Antipruritic effects of the probiotic strain LKM512 in adults with atopic dermatitis. Ann Allergy Asthma Immunol. 113 : 209-216
- Guéniche A. et al (2010) Bifidobacterium longum lysate, a new ingredient for reactive skin. Exp. Dermatol. 19 : 1-8
Paolo Giacomoni, PhD
Insight Analysis Consulting
Paolo Giacomoni acts as an independent consultant to the skin care industry. He served as executive director of research at Estée Lauder and was head of the department of biology with L’Oréal. He has built a record of achievements through research on DNA damage and metabolic impairment induced by UV radiation as well as on the positive effects of vitamins and antioxidants. He has authored more than 100 peer-reviewed publications and has more than 20 patents.