What is obesity?

Obesity and overweight are most often the results of an imbalance between calories taken in and calories expended by the body – in particular, too much fat or sugar relative to actual energy expenditure.^3,4 The resulting excessive increase in body fat can be harmful for health and significantly reduce life expectancy.³ Individuals who are overweight or obese are at greater risk of cardiovascular disease, as well as type 2 diabetes.^5,6 Obesity is also linked to a number of cancers (such as liver and uterine cancer).⁶  Body mass index (BMI) provides an approximate indication of overweight and obesity. WHO considers overweight to equate to a BMI of 25 or more and obesity to a BMI of 30 or above.¹

Repercussions beyond the gut

The balance between energy taken in and energy expended lies partly in bidirectional communication between the gut and the brain - what researchers refer to as the gut-brain axis.¹⁰ This communication between neurons and bacteria is achieved through “signal” molecules which include “short chain fatty acids (sidenote: Short chain fatty acids (SGFA) Short chain fatty acids are a source of energy (fuel) for an individual’s cells. They interact with the immune system and are implicated in communication between the gut and the brain.   Silva YP, Bernardi A, Frozza RL. The Role of Short-Chain Fatty Acids From Gut Microbiota in Gut-Brain Communication. Front Endocrinol (Lausanne). 2020;11:25. ) ” and “neurotransmitters (sidenote: Neurotransmitters Specific molecules that enable communication between the neurons (the nerve cells in the brain), as well as with the bacteria in the microbiota. They are produced by the individual’s cells and by the bacteria in the microbiota.    Baj A, Moro E, Bistoletti M, Orlandi V, Crema F, Giaroni C. Glutamatergic Signaling Along The Microbiota-Gut-Brain Axis. Int J Mol Sci. 2019;20(6):1482. ) ”.^5,6,11 The gut microbiota uses these messengers to help the brain to regulate energy balance, appetite and the feeling of satiety,⁶ and also modulates mood and eating behaviour.^9,10 It can be seen that gut microbiota and obesity are inextricably linked; when the gut microbiota is impaired, it disrupts the digestion, the body’s defence system and the brain, with which it communicates to manage hunger.⁹ Like in a closed electrical circuit, the different “devices”  are connected to one another and allow information (good or bad) to travel between the gut and the brain. 

Can modifying the microbiota help to lose weight?

The solution ought to be straightforward, then: slim down and melt away those extra pounds by looking after your microbiota! The experts will tell you it's not quite that simple, though: it requires an understanding of how diet, probiotics and prebiotics, and faecal microbiota transplant (FMT) influence the ecosystem of our gut microbiota. 

• Diet: Diet is of course the number one risk factor for obesity. It is also the main driver of microbiota modulation. Currently, no categorical link has been established between the effect on intestinal flora and the extent of weight loss.¹² Conversely, the response to a diet is thought to be the result of the initial composition of our intestinal microbiota.^7,11
• Probiotics: Many animal studies show that certain probiotics stand out and are thought to affect metabolic profile, weight gain or satiety in rodents.^2,7,13,14 The results in humans are encouraging: while there is not so much data, certain specific probiotics had an impact on weight, BMI, waist measurement, body fat and metabolic profile.^2,5,6
• Prebiotics: The results for prebiotics differ in humans, whereas their beneficial effects have been widely demonstrated in the laboratory setting2. Generally speaking, studies show that prebiotics have an effect on satiety,⁷ but that there is unfortunately no knock-on effect on weight.²
• Faecal microbiota transplant: Other therapies for modulating gut microbiota are being investigated, including faecal microbiota transplant (FMT), a current treatment for recurrent Clostridioides difficile infection. Researchers are evaluating its potential benefit in correcting dysbiosis and in influencing eating behaviour and energy metabolism.⁷

Colorectal cancer, the importance of environmental factors 

With 694,000 deaths per year around the world, colorectal cancer is the 2nd most deadly cancer. Genetic factors are a significant but minority cause of gastrointestinal cancer, which is most heavily attributed to environmental factors such as sedentary lifestyle, obesity, and, in particular unbalanced diet, which causes intestinal dysbiosis. Furthermore, the hypothesis of an imbalance between harmful and beneficial bacterial species with regard to this cancer is more than likely.

Colorectal cancer doesn’t show any symptoms for a long time, then manifests by persistent or sudden problems with intestinal transit: constipation, diarrhea, the pressing need to go, etc. 

Examining the stool for blood and colonoscopy are the two primary methods for detecting colorectal cancer.

Surgery forms the basis of treatment via the removal of part of the colon, sometimes supplemented with chemotherapy or radiation therapy. 

Bacteria responsible for 80% of stomach cancers

Although various risk factors have been identified (smoking, diet, family history, genetic predisposition), the primary cause of stomach cancer is Helicobacter pylori a pathogenic bacteria that causes chronic gastritis.

The symptoms are not very specific: stomach pain repeated nausea and vomiting, and a change in general state. Only endoscopy of the stomach and esophagus can confirm the diagnosis.

Surgery is the reference treatment for localized tumors, with partial or total removal of the stomach. For locally advanced forms, physicians also add chemotherapy.

Restoring the microbiota, therapy of the future?

Since the existence of a connection between bacteria and gastrointestinal cancers seems more than likely, manipulating the microbiota with probiotics and prebiotics is being studied as a potential therapeutic treatment.  

In 2015, 415 million people had diabetes. According to WHO forecasts, it will be 642 million in 2040. Ninety percent of cases are type 2 diabetes.

Insulin resistance, the primary cause of type 2 diabetes

The primary cause of type 2 diabetes is cells in the body losing their sensitivity to insulin. This resistance to insulin makes the hormone ineffective and leads the pancreas to produce more, to the point of exhaustion. As a result, sugar accumulates in the blood, leading to hyperglycemia and serious long-term complications: myocardial infarction, stroke, arteritis in the lower limbs, kidney failure, and blindness. 

Involvement of the intestinal microbiota?

Although there is a genetic component to type 2 diabetes, lifestyle is the biggest risk factor for the disease--especially sedentism and a diet including too much fat and sugar. Certain fats and sugars set off an inflammatory response associated with metabolic disorders, which in turn increase the level of inflammation. It starts a vicious cycle, in which the gastrointestinal microbiota contributes because it is unbalanced. Researchers have shown that the gastrointestinal microbiota is disrupted in diabetics, and that this dysbiosis contributes to the disease. 

Lifestyle improvements

Above all, diabetes is treated by making lifestyle improvements: weight loss if necessary, regular physical activity, and a balanced diet. It is often necessary to add medication.
The role of certain intestinal bacteria and/or probiotics in diabetes has yet to be confirmed, but their beneficial effects (particularly on appetite and blood sugar) have opened a path for the development of new therapeutic targets for this disease, which affects millions of people.

How do antibiotics unbalance the gut flora?

While antibiotics eradicate the pathogens (sidenote: Pathogen A pathogen is a microorganism that causes, or may cause, disease. Pirofski LA, Casadevall A. Q and A: What is a pathogen? A question that begs the point. BMC Biol. 2012 Jan 31;10:6. ) responsible for infection, they can also destroy some of the beneficial bacteria in your microbiota, systematically causing an imbalance of varying degrees in this ecosystem. This imbalance (known as dysbiosis (sidenote: Dysbiosis Generally defined as an alteration in the composition and function of the microbiota caused by a combination of environmental and individual-specific factors. Levy M, Kolodziejczyk AA, Thaiss CA, et al. Dysbiosis and the immune system. Nat Rev Immunol. 2017;17(4):219-232.   ) ) causes AAD, as the gut microbiota is less able to perform its protective functions. AAD can affect up to 35% of patients^1-3 and up to 80% of children receiving antibiotic treatment.¹

Furthermore, while the gut microbiota shows a certain degree of resilience (i.e. it reverts to a composition similar to that existing before the antibiotic-induced imbalance), it does not always fully recover.^4,5 Recent research has shown that antibiotics can alter the diversity and abundance of bacteria, and that this imbalance can be prolonged (usually 8-12 weeks after the end of treatment).^1,6

In most cases, diarrhea without further symptoms 

The main short-term consequence of antibiotic treatment is the altered bowel movements experienced by some patients, most often resulting in diarrhea. AAD is defined as three or more very loose or liquid stools within 24 hours of the beginning of antibiotic treatment or up to 2 months after its cessation.^7-9 Its incidence depends on several factors, including age, context and the type of antibiotic. The diarrhea is usually mild to moderate in intensity and in the vast majority of cases is functional, i.e. associated with a gut microbiota imbalance.¹ Antibiotics with the broadest spectrum of antimicrobial activity (i.e. that act on a very wide range of bacteria) are associated with higher rates of diarrhea.³

However, in 10%-20% of cases the diarrhea results from an infection by Clostridioides difficile (C. difficile), a bacterium that can become pathogenic due to certain factors, such as antibiotic use, being older than 65 or being affected by certain associated conditions.³ The colonization of the gut microbiota by this bacterium triggers an inflammatory reaction, with clinical consequences ranging from moderate diarrhea to much more serious symptoms, including death.³

Is ending antibiotic use the most effective treatment?

The management of AAD depends on the symptoms and the pathogen (e.g. C. difficile).¹⁰ For mild to moderate diarrhea, treatment involves ending antibiotic use (or replacing the antibiotic with one less likely to cause diarrhea) to allow the microbiota to recover and the patient to rehydrate.¹⁰

Numerous studies have shown that probiotics may help reconstitute the gut microbiota, while some probiotics have proven effective in preventing and treating AAD.^6,11,12 When taken during antibiotic treatment, other probiotics have been shown to reduce the risk of primary and secondary infection with C. difficile.^13-15 Lastly, fecal microbiota transplantation (naturally transferring a healthy microbiota into a sick individual in order to restore his or her microbial ecosystem) is currently only used for the most serious infections, i.e. relapses of infections with C. difficile.^16,17

BMI-21.28

What is infantile colic?

Infantile colic is characterized by excessive crying for unknown reasons in otherwise healthy infants. Gastrointestinal disorders (e.g. immaturity of the gastrointestinal tract, an allergy or intolerance to cow’s milk, stomach reflux)² are mainly to blame,³ but other causes unrelated to the gastrointestinal system,³ such as parental stress,⁴ or maternal smoking, have also been studied.²

Colic is common in babies, but its symptoms, such as persistent crying, can cause distress in parents.

What are the symptoms of infantile colic?

The baby cries a lot, is inconsolable, grimaces and may have a red face. It keeps its fists clenched and may have gas.⁵ Pediatricians have long used the “rule of three” to diagnose infantile colic.⁶ Introduced in 1954, these criteria have since been adapted by an international organization to give a new definition with the following criteria: recurrent and prolonged periods of restlessness, crying or irritability without obvious cause such as stunted growth, fever or ill health, and which cannot be prevented or resolved by the caregivers.⁷

What is the gut microbiota’s role?

A link between infantile colic and the gut microbiota – also known as the gut flora – has recently been established.⁸ Studies have shown that the gut microbiota of infants affected by colic differs from that of other babies:⁹

• Their microbiota is less rich in beneficial bacteria, particularly bifidobacteria (sidenote: Bifidobacterium A genus of Y-shaped bacteria, most species of which are beneficial to humans. They are found in the gut of humans, and in some yogurts.
  
  They:
  - Protect the gut barrier 
  - Participate in the development of the immune system and help fight inflammation 
  - Promote digestion and improve symptoms of gastrointestinal disorders Sung V, D'Amico F, Cabana MD, et al. Lactobacillus reuteri to Treat Infant Colic: A Meta-analysis. Pediatrics. 2018 Jan;141(1):e20171811.  O'Callaghan A, van Sinderen D. Bifidobacteria and Their Role as Members of the Human Gut Microbiota. Front Microbiol. 2016 Jun 15;7:925. Ruiz L, Delgado S, Ruas-Madiedo P, et al. Bifidobacteria and Their Molecular Communication with the Immune System. Front Microbiol. 2017 Dec 4;8:2345. ) and lactobacilli (sidenote: Lactobacilli Rod-shaped bacteria whose main characteristic is the production of lactic acid, from where they get the name “lactic acid bacteria”.  Lactobacilli are present in the oral, vaginal and gut microbiota of humans, but also in plants and animals. They are found in fermented foods, such as dairy products (e.g. certain cheeses and yoghurts), pickles, sauerkraut, etc. Lactobacilli are also found in probiotics, with certain species recognized for their beneficial properties.   W. H. Holzapfel et B. J. Wood, The Genera of Lactic Acid Bacteria, 2, Springer-Verlag, 1st ed. 1995 (2012), 411 p. « The genus Lactobacillus par W. P. Hammes, R. F. Vogel Tannock GW. A special fondness for lactobacilli. Appl Environ Microbiol. 2004 Jun;70(6):3189-94. Smith TJ, Rigassio-Radler D, Denmark R, et al. Effect of Lactobacillus rhamnosus LGG® and Bifidobacterium animalis ssp. lactis BB-12® on health-related quality of life in college students affected by upper respiratory infections. Br J Nutr. 2013 Jun;109(11):1999-2007. ) ,⁸ which can modulate immune responses to protect against colic.⁵
• Instead, their microbiota appears to be colonized by Escherichia coli,⁵ Klebsiella or other potentially pathogenic species.⁵

This gut microbiota imbalance, known as a “dysbiosis (sidenote: Dysbiosis Generally defined as an alteration in the composition and function of the microbiota caused by a combination of environmental and individual-specific factors. Levy M, Kolodziejczyk AA, Thaiss CA, et al. Dysbiosis and the immune system. Nat Rev Immunol. 2017;17(4):219-232.   ) ”, appears to be strongly linked to colic: according to one hypothesis, an altered gut microbiota composition modifies intestinal motility (the way in which food moves through the digestive system), resulting in excessive production of gas.⁵

How to help babies... and parents?

The family doctor is still the first port of call to diagnose infant colic and reassure parents. There is no cure¹⁰ for colic, but a few simple daily practices can help relieve the symptoms. These include breastfeeding, carrying your baby and balancing your child’s gut microbiota, particularly using probiotics.⁵ Probiotics appear to be a promising avenue, since the intake of “good” bacteria for a few months may reduce gut inflammation⁶ and help shorten the daily duration of crying.¹¹ Since they help maintain a good intestinal balance, probiotics can also be used as a preventative measure.⁵

BMI-21.18

What is a vaginal yeast infection?

A vaginal yeast infection is an infection of the vulva and the vagina caused by a yeast-like fungus, in most cases Candida albicans³. After bacterial vaginosis, it is the second most common infectious vaginal disease.¹ It is important to consult a doctor to confirm diagnosis, since its symptoms are not very specific. The most common clinical symptoms are abnormal vaginal discharge (leukorrhea), genital itching, and a burning sensation accompanied by vaginal pain or irritation that can lead to dyspareunia (sidenote: Dyspareunia Recurrent or persistent genital pain during sexual intercourse. ) or dysuria (sidenote: Dysuria Painful urination, often described by the patient as a burning, tingling or itching sensation. ) .¹

Is the vaginal microbiota involved?

Every woman’s vaginal microbiota is unique and, unlike other microbiota, the vaginal microbiota is well-balanced when its diversity is low⁴ Species of the genus Lactobacillus (sidenote: Lactobacilli Rod-shaped bacteria whose main characteristic is the production of lactic acid, from where they get the name “lactic acid bacteria”.  Lactobacilli are present in the oral, vaginal and gut microbiota of humans, but also in plants and animals. They are found in fermented foods, such as dairy products (e.g. certain cheeses and yoghurts), pickles, sauerkraut, etc. Lactobacilli are also found in probiotics, with certain species recognized for their beneficial properties.   W. H. Holzapfel et B. J. Wood, The Genera of Lactic Acid Bacteria, 2, Springer-Verlag, 1st ed. 1995 (2012), 411 p. « The genus Lactobacillus par W. P. Hammes, R. F. Vogel Tannock GW. A special fondness for lactobacilli. Appl Environ Microbiol. 2004 Jun;70(6):3189-94. Smith TJ, Rigassio-Radler D, Denmark R, et al. Effect of Lactobacillus rhamnosus LGG® and Bifidobacterium animalis ssp. lactis BB-12® on health-related quality of life in college students affected by upper respiratory infections. Br J Nutr. 2013 Jun;109(11):1999-2007. ) dominate the vaginal microbiota,⁴ but yeasts such as Candida albicans are also found in smaller quantities.⁵

The vaginal ecosystem evolves over the course of a woman’s life.⁶ This change is normal and is influenced by the menstrual cycle, puberty and the menopause, sexual activity, contraception, intimate hygiene, and pregnancy.^7,8,9

A dysbiosis (sidenote: Dysbiosis Generally defined as an alteration in the composition and function of the microbiota caused by a combination of environmental and individual-specific factors. Levy M, Kolodziejczyk AA, Thaiss CA, et al. Dysbiosis and the immune system. Nat Rev Immunol. 2017;17(4):219-232.   ) is when the vaginal ecosystem is unbalanced (due to antibiotic treatment, douching, stress, smoking, etc.)^2,6: species of Lactobacillus no longer predominate and instead certain opportunistic (sidenote: Opportunistic infection An infection caused by a microorganism that is normally non-pathogenic, but which becomes so when the host microbiota loses its balance (through factors such as a weakened immune system, disease, age, certain medication, etc.). ) species may proliferate. This is what happens with vaginal candidiasis: Candida – yeasts normally present in the vagina and the gut⁵ – proliferate abnormally and become pathogenic under specific conditions. It is estimated that 10%-30% of women contract yeast infections following antibiotic treatment.¹⁰

Other factors that can increase the risk of infection¹ include corticosteroid use, pregnancy, immunosuppressive diseases, poorly controlled diabetes, oral contraception, and IUD. Many factors have been identified but the mechanisms are not yet fully understood.¹¹

Antifungals and probiotics

The classic treatment for vaginal yeast infections is antifungal medication administered orally or topically.¹¹ However, relapses can occur and new therapeutic approaches are currently being evaluated.¹¹ Recent work suggests that oral or topical probiotics (capsules or vaginal suppositories) may rebalance the vaginal microbiota and reduce the frequency of relapse.^12,13

To reduce the risk of infection, certain intimate hygiene practices are recommended¹⁴ – daily habits to help care for your vaginal microbiota.  

BMI-21.21

What is bacterial vaginosis?

Bacterial vaginosis is a harmful and hard to detect disorder. 50% of women are asymptomatic, while others suffer from local irritation or foul-smelling discharge.³

In practice, doctors use the Amsel score⁴ to diagnose bacterial vaginosis. Diagnosis is based on the presence of at least three of the following criteria:

• Thin, homogeneous vaginal discharge 
• A vaginal pH above 4.5 
• An amine smell (similar to a fishy smell) after a specific test is performed on a vaginal smear
• Presence of vaginal tissue cells coated with bacteria when discharge is examined microscopically

Many risk factors are associated with the disease, including age, menstrual cycle, pregnancy, and sexual history, but also vaginal douching and smoking.³ A vaginal dysbiosis induced by antibiotic treatment may also participate in the development of bacterial vaginosis, creating a vicious circle, since antibiotics can be used to treat the infection.³

Lastly, women with bacterial vaginosis are more likely to contract sexually transmitted infections (STIs), including herpes, HPV, AIDS and bacterial infections.^5,6

Is there a link with the vaginal microbiota?

Bacterial vaginosis is associated with an imbalance (dysbiosis (sidenote: Dysbiosis Generally defined as an alteration in the composition and function of the microbiota caused by a combination of environmental and individual-specific factors. Levy M, Kolodziejczyk AA, Thaiss CA, et al. Dysbiosis and the immune system. Nat Rev Immunol. 2017;17(4):219-232.   ) ) of the vaginal microbiota.² The vaginal microbiota is dominated by different species of the bacterial genus Lactobacillus (sidenote: Lactobacilli Rod-shaped bacteria whose main characteristic is the production of lactic acid, from where they get the name “lactic acid bacteria”.  Lactobacilli are present in the oral, vaginal and gut microbiota of humans, but also in plants and animals. They are found in fermented foods, such as dairy products (e.g. certain cheeses and yoghurts), pickles, sauerkraut, etc. Lactobacilli are also found in probiotics, with certain species recognized for their beneficial properties.   W. H. Holzapfel et B. J. Wood, The Genera of Lactic Acid Bacteria, 2, Springer-Verlag, 1st ed. 1995 (2012), 411 p. « The genus Lactobacillus par W. P. Hammes, R. F. Vogel Tannock GW. A special fondness for lactobacilli. Appl Environ Microbiol. 2004 Jun;70(6):3189-94. Smith TJ, Rigassio-Radler D, Denmark R, et al. Effect of Lactobacillus rhamnosus LGG® and Bifidobacterium animalis ssp. lactis BB-12® on health-related quality of life in college students affected by upper respiratory infections. Br J Nutr. 2013 Jun;109(11):1999-2007. ) . These bacteria help maintain an acidic pH in the vagina and thus prevent the proliferation of pathogenic bacteria.⁷ The vaginal microbiota also contains yeasts such as Candida albicans in smaller quantities.⁸

With bacterial vaginosis, this normal microbial flora is replaced by a polymicrobial flora comprising numerous bacteria (Gardnerella, Atopobium, Prevotella, Mobiluncus, etc.).² This leads to an increase in the pH of the vagina (which is normally very acidic), mainly attributed to the decrease in the predominance of Lactobacillus species.⁹ However, the mere presence of species from this polymicrobial flora does not in itself seem to cause infection, i.e. a woman whose vagina contains Atopobium or Prevotella species will not necessarily report symptoms. In fact, Gardnerella vaginalis is present in 90% of symptomatic subjects and 45% of healthy subjects.⁴ For a long time, this bacterium was considered the main pathogen behind bacterial vaginosis, but new research has shown that Gardnerella vaginalis can colonize the vagina without triggering infection.¹⁰ The causes of the infection are yet to be determined and research in the area continues.³

How to avoid bacterial vaginosis

Treatment is only recommended for women who are symptomatic. Recommended treatment currently involves the prescription of oral or vaginal antibiotics.² While antibiotics may help alleviate symptoms, relapse is unfortunately very common.¹¹

However, there are a number of ways to reduce your chances of getting bacterial vaginosis. Firstly, avoid certain risk factors, such as vaginal douching or smoking.³ Vaginal or oral probiotics,^12,13 that restore the balance of the vaginal microbiota can be used to treat or prevent relapses.

BMI-21.22

What is travelers’ diarrhea?

Contrary to popular belief, travelers’ diarrhea is not caused by exotic foods poorly digested by unaccustomed stomachs. It is a real infection most frequently caused by bacteria  (Escherichia coli, Salmonella, Shigella, Campylobacter).² It may also be caused by a parasite (Giardia, Cryptosporidium, etc.)² or a virus (norovirus, rotavirus).² The pathogen responsible for the diarrhea is identified in only 40%-60% of symptomatic travelers.⁴ The main source of the microorganisms involved are contaminated food (especially raw vegetables, undercooked meat or fish, unpeeled fruit, etc.) and contaminated water.⁵ It can also be transmitted through contact with other people when hygiene rules are not respected.⁵

What is the microbiota’s role? 

One of the gut microbiota’s roles is to prevent or limit the invasion of the intestine by pathogens (sidenote: Pathogens A pathogen is a microorganism that causes, or may cause, disease. Pirofski LA, Casadevall A. Q and A: What is a pathogen? A question that begs the point. BMC Biol. 2012 Jan 31;10:6. ) .⁶ Although common, the “tourista” is not without consequences. Regardless of the pathogen, diarrhea disrupts the balance of the gut microbiota at least temporarily, leading to dysbiosis (sidenote: Dysbiosis Generally defined as an alteration in the composition and function of the microbiota caused by a combination of environmental and individual-specific factors. Levy M, Kolodziejczyk AA, Thaiss CA, et al. Dysbiosis and the immune system. Nat Rev Immunol. 2017;17(4):219-232.   ) .¹ This imbalance may have long-term consequences, including an increased risk of developing post-infectious⁷ irritable bowel syndrome, which occurs in 3%-17% of patients.² A research team recently showed that gut microbiota diversity was significantly lower in Swedish travelers who contracted a Campylobacter infection than in travelers who remained uninfected.⁸ Another research team found that diarrhea during travel was associated with a higher relative abundance in the gut of a specific bacteria (Prevotella copri) before departure and after return.⁹ Could travelers’ gut microbiota composition be used to predict the risk of developing diarrhea during the trip? Since there are still very few studies in this area, it remains to be confirmed.

What are the symptoms of traveler’s diarrhea?

The symptoms and duration vary depending on the cause⁴ (bacterial, parasitic or viral), but on average symptoms last 4-5 days without treatment.² In addition to frequent loose or watery stools (at least 3 per day),⁵ at least one of the following symptoms must be present: fever, nausea, vomiting, abdominal cramps or an urgent need to go to the bathroom.² The major risk is dehydration resulting from the loss of fluids through watery diarrhea. At-risk individuals (children, the elderly, or those with chronic conditions that weaken the immune system²) are more likely to be hospitalized.

Definition of travelers' diarrhea:

How to prevent and treat travelers’ diarrhea

The prevention of travelers’ diarrhea mainly involves hygiene measures such as frequent hand washing and food precautions.⁵ Ask your doctor or pharmacist for advice before traveling. Rehydration is key to treating travelers’ diarrhea:⁵ clean water (bottled water, etc.) or herbal teas drunk often and in small quantities. Any lightly sweetened and/or salted food is recommended (solid foods are not contraindicated).⁴ Antidiarrheal drugs help reduce the risk of dehydration and may be recommended in some cases.¹⁰ Antibiotics may also be necessary. However, antibiotics can lead to a reduction in the diversity of the gut microbiota, which thus loses its ability to act as a barrier against pathogens (sidenote: Pathogen A pathogen is a microorganism that causes, or may cause, disease. Pirofski LA, Casadevall A. Q and A: What is a pathogen? A question that begs the point. BMC Biol. 2012 Jan 31;10:6. ) . Moreover, antibiotic use can lead to the selection of antibiotic-resistant bacteria.¹¹ For this reason, they are only recommended for severe diarrhea, and in some cases for moderate diarrhea,¹⁰ under the supervision of a doctor. Probiotics may be useful as a preventive measure¹², and to limit the intensity and duration of symptoms.^13,14

BMI 21.20

What exactly is the skin microbiota?

Let’s start by focusing on the skin, the largest organ in the human body and its first line of defense. The skin acts as a triple protective barrier:^1,2

• a physical barrier that protects the internal organs from the external environment³
• a chemical barrier: dry and rich in salt and acidic compounds, the skin is a hostile environment for many microorganisms⁴
• an immune barrier, thanks to defense cells in the skin that prevent colonization and infection by pathogenic microbes²

Despite this, the skin is home to its own distinctive microbiota which includes bacteria (Cutibacterium acnes, Staphylococcus epidermidis, etc.), fungi (e.g. Malassezia), viruses (e.g. papillomavirus) and parasites (including mites such as Demodex). These microorganisms live in perfect harmony and together form the skin microbiota.^1,5

As you may have noticed, your skin changes from one part of the body to another: 

• drier on the forearm and the palms of the hand.^1,5
• oilier on the face, chest and back.^1,5
• and more humid in the armpits, the elbow fold, the nostrils, on the back of the knee and on the groin.^1,5

Each of these skin sites is home to a distinct microbiota adapted to its specific environment¹. Some researchers also distinguish a fourth site in the foot (nails, heel and space between toes).¹
In addition to these variations across the skin’s surface, there are also variations according to depth or skin layer: the deeper you go into the dermis, the fewer the microorganisms (sidenote: Microorganisms Living organisms too small to see with the naked eye. This includes bacteria, viruses, fungi, archaea, protozoa, etc., collectively known as ’microbes’. Source: What is microbiology? Microbiology Society. ) and the more similar these microorganisms are from one person to next.⁶

How does the skin microbiota change throughout life?

The skin microbiota is relatively stable over time^1,5 and only changes at the major stages of life. 

At birth, children born vaginally are passed on vaginal bacteria (Lactobacillus, C. albicans), while those born by caesarean section receive skin microbes (Staphylococcus, Streptococcus). At puberty, the rate of secretion of growth hormones explodes. The skin becomes oilier and selects more well-adapted microorganisms that live on through adulthood. The skin gradually changes as it ages, with a weakened immune system, reduced cell renewal, less sweat, and altered sebum production.^7,8

These physiological changes modify the skin environment and alter the microbial balance⁷, which becomes more diverse and sees a change in dominance in bacterial groups.⁸

Why is the skin microbiota a key factor in skin health?

The skin microbiota knows how to thank its host for giving it food and shelter. It protects the host from pathogens (sidenote: Pathogens A pathogen is a microorganism that causes, or may cause, disease. Pirofski LA, Casadevall A. Q and A: What is a pathogen? A question that begs the point. BMC Biol. 2012 Jan 31;10:6. ) through its physical presence on the skin and by secreting antibacterial molecules and acids.² But that’s not all. The skin microbiota also plays a key role in immunity: it stimulates the immune defense mechanisms of the epidermis and the body as a whole and calms inflammation where necessary.⁴

What diseases are associated with an unbalanced skin microbiota?

The composition of the skin microbiota is mostly influenced by host characteristics (age, sex, genes, immune status, diet, stress levels) and the environment (lifestyle, domestic and personal hygiene, living arrangements, geographical location, sun exposure, etc.).² At times, factors such as stress, a lifestyle change or the use of medication (e.g. antibiotics) or personal hygiene products disrupt the balance of the microbiota: bacteria previously beneficial to the host take the upper hand and become pathogenic.¹ Many common skin diseases are associated with changes in the microbiota. This situation is known as a dysbiosis (sidenote: Dysbiosis Generally defined as an alteration in the composition and function of the microbiota caused by a combination of environmental and individual-specific factors. Levy M, Kolodziejczyk AA, Thaiss CA, et al. Dysbiosis and the immune system. Nat Rev Immunol. 2017;17(4):219-232.   ) .¹

Dysbiosis is often associated with pathological skin conditions such as acne,⁹ atopic dermatitis,¹⁰ psoriasis,¹¹ seborrheic dermatitis,¹² rosacea¹³ or skin cancer.¹⁴ Changes in the skin microbiota can also be observed in non-pathological skin conditions such as sensitive skin, sensations of discomfort or irritation, or diaper rash. The skin is constantly exposed to various external factors linked to lifestyle (cold, heat, sun, UV, hygiene products, etc.) or the individual (genes, sensitivity, allergies, etc.) that can affect the physical, mechanical or microbial properties of the skin barrier.¹⁵ The microbiota is also involved in wound healing¹⁶ and body odor.¹⁷

How can you take care of your skin microbiota? 

You now know the importance of the skin microbiota for the health of your skin, and that the gut microbiota also plays a role in skin health. So how can you take care of the various microbiota so that your skin stays healthy? Many researchers have looked into this question. Unfortunately, the answer isn’t as straightforward as using beneficial bacteria or yeast to replenish or enrich the existing microbiota or replace a microbiota that’s not up to the job. Instead, the idea is to modify the microbiota so that it functions correctly, thus improving host health. How? There are several ways to improve the balance and diversity of the gut microbiota, each with its own characteristics:

Oral preparation: 

The existence of a gut-skin axis raises hope that we may be able improve the health of the skin by modulating the gut microbiota by taking probiotic, prebiotic and symbiotic supplement or through a better diet:

• Probiotics are living microorganisms that confer a health benefit on the host when applied in appropriate quantities^19,20. For certain inflammatory skin diseases, the use of specific probiotics appears to be effective.¹⁴
• Prebiotics are specific non-digestible dietary fibers that confer a health benefit. They are selectively used by beneficial microorganisms in the host microbiota.^21,22 Symbiotics²³ mixture containing both prebiotic and probiotic have shown promising results in atopic dermatitis.²⁴
• Diet, the diversity and quality of what we eat contributes to the balance of our gut microbiota.^25,26 A poorly balanced diet can affect the composition of the gut and give rise to certain conditions.²⁷ To keep our gut in shape we should know what foods have a beneficial or adverse effect on it.²⁸

Topical preparations

While few studies existed, products applied to the skin that contain certain probiotics, prebiotics or both, have shown positive resulted in improving the skin's health of patient with skin condition.^14,24

However, clinical trials are still required to optimize their formulation. Hence the importance of following our latest news on the skin microbiota.

BMI-21.13

The term ENT includes three parts of the body: Ears, Nose, and Throat (which also includes the mouth).

• The oral microbiota brings together more than 700 bacterial species, which contribute to oral health (teeth, gums, tongue, etc.) and, more generally, to overall health. A disruption in this equilibrium (dysbiosis), resulting from poor oral hygiene, a drop in immunity, or a genetic origin may lead to local infections (cavities, periodontitis, etc.) that are likely to migrate or cause more serious diseases, such as cardiovascular diseases. Hygiene and dental care remain the most effective method of prevention.
• In the ear canal, the composition of the auricular microbiota is closely related to that of the skin. Recent work has shown the harmless presence of Alloiococcus otitis and Corynebacterium otitidis, two bacterial species that until now have only been associated with middle ear infections. This discovery suggests that the ear canal serves as an infectious reservoir for the middle ear.
• Although close to the oral microbiota, the nasopharyngeal microbiota, which covers the nasal airways and the pharynx, is composed of very different germs.

Analyzing the realm of ENT and its microbiota may enable early diagnosis for various diseases that appear because of dysbiosis (sidenote: Dysbiosis Generally defined as an alteration in the composition and function of the microbiota caused by a combination of environmental and individual-specific factors. Levy M, Kolodziejczyk AA, Thaiss CA, et al. Dysbiosis and the immune system. Nat Rev Immunol. 2017;17(4):219-232.   ) and may also contribute to the development of personalized medicine based on probiotics.

The Biocodex Microbiota Institute is dedicated to education about human Microbiota for General Public and Healthcare Professionals, it doesn't give any medical advice.
We recommend you to consult a healthcare professional to answer your questions and demands.