Patients affected by kidney failure often suffer from severe metabolic disorders. Diabetes is the leading cause of end-stage kidney disease and subsequent renal transplants (RT), while 20% of patients who were normoglycemic prior to RT develop New-Onset Diabetes After Transplant (NODAT) within one year of their operation. The immunosuppressive treatment received by patients following RT is largely held responsible, since it is known to induce insulin resistance, but this does not explain why some patients are more resistant to the development of NODAT than others.

The gut microbiota suspected

A French team compared the fecal microbiota of 50 subjects with kidney failure before and (3 to 9 months) after RT. 16 of the subjects had type 2 diabetes (T2D) prior to transplantation, 15 developed NODAT and the remaining 19 (control subjects) were not diabetic before or after RT. The researchers focused on nine bacterial markers (sidenote: Firmicutes/Bacteroidetes ratio, Bacteroides-Prevotella group, Lactobacilli, Bifidobacteria, Akkermansia muciniphila, Faecalibacterium prausnitzii, Escherichia coli, Clostridium coccoides and Clostridium leptum. ) already linked to diabetes or metabolic disorders in mice and/or patients who have not received a kidney transplant.

Pre- and post-transplant differences

Prior to RT, Lactobacillus sp. was less frequently detected in control subjects (60%) than in NODAT patients (87.5%) or patients with T2D pre-transplant (100%). Following RT, its relative abundance increased by a factor of 20 and 25 in the NODAT and T2D groups, respectively. On the other hand, Akkermansia muciniphila decreased by a factor of 2,500 in the NODAT group and 50,000 in the T2D group. However, these alterations were not observed post-transplantation in the control subjects. Lastly, prior to RT, the relative abundance of Faecalibacterium prausnitzii was 30 times lower in T2D patients than in the control subjects.

A pre-transplant dysbiosis responsible for NODAT?

The authors’ conclusions? A dysbiosis prior to RT (characterized among other things by the presence of lactobacilli) may predispose patients to the development of NODAT, in the context of the consumption of immunosuppressive drugs favoring its onset. Larger-scale prospective studies not limited to the nine bacterial markers considered here will make it possible to describe in greater detail the role of the intestinal microbiota in the development of NODAT.

“An apple a day keeps the doctor away.” The explanation behind this old saying can be found in the abundance of vitamins, minerals and other antioxidants in this fruit, but not solely: apples are also an important source of microorganisms (bacteria, viruses, fungi) with many health benefits, which colonize and temporarily enrich our gut microbiota. Few studies have discussed these “good” microbes since most of them focus on microorganisms responsible for foodborne illness. This oversight has been corrected thanks to an Australian team, whose findings are published in the Frontiers in Microbiology journal.

Organic food provides greater diversity

Researchers analyzed all microorganisms hidden in flesh, skin, stem and seeds of apples, as well as the impact of the cultivation method used. Their first observation was that most bacteria are concentrated in the stem, seeds and calyx, which we usually do not eat. But flesh and skin also contain higher concentrations of bacteria. Another finding from the study was that the microbiota of organic apples while not more abundant was much more diversified and more homogeneous than that of conventional apples. This could limit the presence of harmful microorganisms that may cause foodborne illness. And good news: diversity was highest in the organic fruit’s flesh.

Bacteria that are good for our health

The study out of Australia also showed that organic apples mainly contain lactobacilli, with well-known beneficial properties, as well as another bacterial type responsible for the taste of strawberries. As to the microbiota of ordinary apples, it is strongly dominated by Enterobacteriaceae, a family of bacteria including some species (such as Escherichia coli) that are responsible for foodborne illness. The authors believe that these differences in microbial composition are due primarily to agricultural practices and storage conditions. And they hope to see, one day, this nutritional profile indicated on marketing labels, together with the content of macronutrients, vitamins and minerals.

Although it is by far the most well-known microbiota, as it is the most important and most studied, the gut microbiota is not the only microbial community in our body. Bacteria, viruses and yeasts colonize all our bodily fluids, even the most intimate. A team of American researchers has set out to identify and analyze the microorganisms present in semen using a technique normally used to assess whether genes are functional. Their aim was to determine whether this approach is suitable for evaluating the diversity of the microbiota in semen.

Less rich but more diverse than vaginal microbiota

The microorganisms residing in the male genital tract come mainly from direct contact with women during sexual intercourse. Escherichia coli, which is linked to genital and urethral infections, is the most frequently observed bacterium. The male genital microbiota shares 85% of its bacterial species with the vaginal microbiota but is less abundant and more diverse.

An infected sample

The researchers analyzed the semen of 85 men who were in a heterosexual relationship. The technique used by the researchers made it possible to identify the main bacteria colonizing the male genital tract. Only one sample had a very different microbial mix, showing a particularly high content in Streptococcus agalactiae. This bacterial species is responsible for sexual infections in both men and women and may lead to miscarriage or stillbirth in the latter. Its abundance is difficult to explain, with the most likely cause being infection via the subject’s partner.

An effective diagnostic technique

The authors conclude that this new method appears just as effective in diagnosing bacterial colonization or infection of semen as the method traditionally used to analyze human microbiota.

Fasting and its effects on the makeup of the intestinal microbiota have been the subject of very few studies because they are difficult to model. However, since diet is one of the main environmental factors that can shape our gut microbiota, it is not hard to imagine that prolonged food deprivation may change the composition of this microbial community. Accordingly, a team of Turkish researchers carried out a small study with nine Muslim subjects (seven women and two men) who fasted during Ramadan. A pillar of Islam, this age-old practice involves abstaining from food and drink from sunrise to sunset for a period of 29 days. In the study, conducted between 18 June and 16 July 2015, daily fasts lasted 17 hours.

A healthier gut microbiota

At the end of Ramadan, stool samples obtained from the participants showed a higher abundance of the good bacteria Bacteroides fragilis and Akkermansia muciniphila. The latter group makes up 3%-5% of the microbial community in healthy individuals but this proportion is lower for the obese. Conversely, the abundance of other bacteria decreased, although not significantly. Fast also resulted in a reduction in total cholesterol and fasting blood sugar levels, confirming the results of another study. However, the authors did not observe the significant decrease in participants’ BMI (sidenote: Body Mass Index.  Ratio of weight in kg to square of height in sq.m ) * seen in other studies, presumably because of the small number of subjects involved.

Resistance to change

The authors suggest that the improved makeup of the gut microbiota after fasting is due to the resistance of beneficial bacteria species, such as Bacteroides and Akkermansia, to dietary changes. These results are preliminary and require confirmation in larger studies, but they provide a better understanding of the relationship between fasting and the intestinal microbiota.

A look at oranges under a magnifying glass

Oranges and citruses are not only known for their high content of ascorbic acid (vitamin C) and carotenoids, but they also are a major source of flavonoids–which have antioxidant, anti-inflammatory, antitumoral and lipid-lowering properties. These fruits are believed to preserve our health and protect us from chronic diseases.

30 cl of orange juice per day

In a small clinical trial, researchers from São Paulo measured the effects of the daily consumption of pasteurized orange juice on the composition of the gut microbiota and the metabolism of 10 healthy young women. During the first month, participants were instructed to drink and eat according to their dietary habits, but avoiding sources of flavonoids, prebiotics and probiotics, as well as alcoholic beverages. The objective was to start the experimental period with low contents of tested substances in order to measure the effect of citruses. During the next two months, they had to drink 30cl of industrial orange juice every day; and the last month they resumed their dietary habits but excluding orange juice. Blood and stool samples were taken, and several biological parameters were measured at the end of each period.

Microbiota enriched with “good” bacteria

Daily consumption of orange juice led to a significant drop in glucose, insulin, triglycerides, total cholesterol, LDL-cholesterol (“bad” cholesterol) levels, as well as in insulin resistance. Gut microbiota had a higher abundance of some microorganisms, especially species able to grow in the absence of oxygen (“anaerobic” microorganisms), as well as lactobacilli and bifidobacteria which have health benefits. While ammonium production, rather harmful to the intestines, temporarily dropped, the production of molecules that are indicative of a healthy microbiota increased. The authors concluded that orange juice could thus act as a prebiotic, by promoting the growth or activity of gut bacteria that are beneficial to our health, and they urge us to drink it daily.

Each year, early puberty affects 20 out of every 10,000 girls worldwide, with childhood obesity increasing the risk of occurrence. Since 2010, greater attention has been paid to the effects of the intestinal microbiota on energy homeostasis and obesity. Although many factors may influence the gut microbiota (use of antibiotics, etc.), breastfeeding seems to play a primary role in its development. Researchers have therefore manipulated the diet of lactating female mice in order to assess the influence of diet on the risk of obesity and early puberty among their offspring. For three weeks from the birth of their pups, female mice were fed either a normal calorie diet (NCD) containing 12% fat or a high-fat diet (HFD) containing 60% fat. 21 days after birth, all the young mice were weaned, fed a normal calorie diet and randomly placed in cages alongside four young mice from NCD mothers, four young mice from HFD mothers or two young mice from NCD mothers and two young mice from HFD mothers. The goal was to measure the impact of this cohabitation and assess whether it reversed any effects of a maternal high-fat diet upon offspring.

Impact of maternal diet during breastfeeding

A high-fat diet for mothers during lactation influenced the development of their offspring’s microbiota. For example, there was an increase in the proportion of Streptococcaceae and Peptostreptococcaceae in the intestinal microbiota of the young mice. In addition, the offspring of HFD mothers had microbiota with significantly less richness. A maternal high-fat diet also resulted in childhood obesity, early puberty, irregular menstrual cycles and signs of impaired glucose metabolism in female offspring. However, early puberty was not observed in young males.

Effects of sharing microbiota

Since mice are coprophagous animals, they share their microbiota via the fecal-oral route. Following cohabitation with the offspring of NCD mothers, the offspring of HFD mothers saw the abundance of their microbiota increase, reversing the effects of the maternal high-fat diet. This also protected females against early puberty and insensitivity to insulin. However, no protective effect was observed on the weight or body fat of HFD offspring.

A new therapeutic approach for metabolic disorders?

According to the authors, breastfeeding plays a critical role in the development of a normal metabolic and reproductive function among offspring. Insulin resistance associated with a microbiota dysbiosis increases the likelihood of early puberty where this results from a high-fat maternal diet during breastfeeding. Consequently, microbiota may represent a new therapeutic target in the treatment of metabolic and reproductive disorders.

Several studies have shown that sleep is highly dependent on the quality of the gut microbiota, with which it is constantly interacting. While a depletion in bacterial flora leads to a decrease in sleep duration, chronic sleep disorders or alterations of the sleep-wake rhythm lead in turn to an imbalance of the microbiota (called “dysbiosis”).

Butyrate: a sleep-promoting agent?

Butyrate is a substance produced by the fermentation of dietary fiber under the influence of the gut microbiota. According to a new study published in the Scientific Reports journal, it seems to play a major role in sleep onset and sleep quality...Researchers from the University of Washington aimed at identifying molecules used as sleep-inducing signals. They focused primarily on butyrate, a short-chain fatty acid mainly found in dairy products and fiber from many plants (asparagus, oat flakes, artichokes, raw garlic, leeks, onions). When produced by the intestines under the action of specific bacteria, butyrate enters into the portal vein, a large blood vessel that transports it to the liver, where it is stored. According to the researchers’ hypothesis, it acts on the portal vein’s sensory mechanisms in order to promote sleep.

Increase in deep sleep

Butyrate was thus tested in rodents according to three modes of administration. Subcutaneous injection, which is supposed to act on the entire organism, had no effect. On the contrary, oral administration increased the duration of deep sleep (sidenote: Deep sleep Sleep phase ensuring optimal recovery of the body. ) by around 50%, decreased body temperature, and reduced episodes of paradoxical sleep (sidenote: paradoxical sleep Also known as REM sleep (Rapid Eye Movement); it is the last phase of a complete sleep cycle and it is when we dream. ) . Direct injection into the portal vein had similar, but enhanced, effects, confirming the involvement of the liver in the process.

Eat better to sleep better!

Butyrate seems to trigger sleep by binding to receptors located on the wall of the liver and/or portal vein. Taking care of your gut microbiota by consuming foods that contain butyrate (dairy products, butter and cheese for example) or promote the production of butyrate could thus improve sleep disorders. It is probably a healthier and more natural solution than sleeping pills!

Recommended by our community

Despite progress regarding prevention, dental caries or cavities remain one of the most common afflictions in the world. They are formed when acid attacks the tooth enamel following the fermentation of dietary sugars by microbes found in dental plaque. While pathogenic bacteria implicated in this process are well known, the role of fungi contained in oral microbiota is not fully understood.

Candida dubliniensis is associated with cavity severity

To better understand how microorganisms interact to form a cavity, an American research team investigated dental plaque microbiota at different stages of cavity development. Their study, published in the review Applied and Environmental Microbiology, included 33 children with varying cavity status: some had no cavities, others had a few cavities which were attacking the enamel, others had cavities which had reached the dentine.

The authors identified 139 species of fungi. The two most abundant belonged to the Candida family: Candida albicans and Candida dubliniensis. They observed that composition of dental plaque microbiota varied significantly depending on cavity status, with an overabundance of 4 species in children with cavities and of 12 other species in children with healthy teeth. More specifically, the content of C. dubliniensis was directly correlated to cavity severity. Some of the beneficial species were able to mitigate the role of Staphylococcus mutans in tooth decay (a bacterium implicated in cavity formation) via the production of xylitol and antimicrobial compounds.

New therapeutic perspectives?

C. dubliniensis is known to play a role in cavity progression and severity and could be a good risk predictor for dental caries, concluded the authors. Their work should open up new preventive and therapeutic perspectives for dental caries.

Reduced risk of premature birth, improvement of maternal mood, better development of the brain, vision, motor skills, heart and immune system in newborns: the consumption of omega-3 oils (naturally present in salmon, mackerel, eggs, spinach, avocado and more) is favorable to the health of both mothers and their babies! This is why health authorities recommend that pregnant women consume between two and three portions of fish per week. This upper limit is fixed because of the risks associated with ingestion of mercury, found in varying quantities in fish. What is the impact of this dietary recommendation on the gut microbiota of newborns?

A microbiota affected by the maternal diet

To find out, a team of researchers analyzed stool samples from around one hundred babies aged around 4 months on average. Their results revealed three gut microbiota profiles: one dominated by bifidobacteria–also the richest and most diverse, one dominated by Escherichia spp., and the last by another specific bacterium, i.e. Enterobacter. Infants whose mother followed the dietary recommendations during the third trimester (at least 2 portions of fish per week) were up to 5 times more likely to have a microbiota dominated by bifidobacteria than by Escherichia. Could this protect them against certain diseases? It is possible, according to certain studies indicating that a microbiota with a low content of bifidobacteria is associated with irritable bowel syndrome, inflammatory bowel disease, celiac disease, and more.

Validity of the dietary recommendations

The authors consider that this study confirms the validity of dietary recommendations regarding consumption of fish during the third trimester of pregnancy–a critical period for brain development–revealing a benefit unknown until now. According to the authors, understanding the impact of the maternal diet on the infant gut microbiota should help better define the dietary recommendations for pregnant women.

The relationship between asthma and the microbiota in the respiratory tract of asthmatic children is still poorly understood. A prospective study analyzed the links between the relative abundance of bacteria in 319 nasal samples collected at two points in time–with asthma under control and at the onset of an attack–and asthma attacks suffered by 254 school-age children with Stage 2 asthma, 75.7% of whom experienced an attack during the 320 days of follow-up (with two attacks for 43.4% of the children included in the follow-up period).

Bacterial groups linked to asthma risk

The results show that the risk of attack or exacerbation varies according to the type of bacteria colonizing the nasal tract. Specifically, microbiotas in which the Corynebacterium and Dolosigranulum genera prevail are associated with a lower risk of asthma attack than microbiotas dominated by more pathogenic bacteria, particularly the Staphylococcus, Streptococcus and Moraxella genera. Furthermore, a shift to Moraxella at the onset of an attack (peak expiratory flow in the yellow zone) is associated with a higher risk of exacerbation. These results are consistent with those of previous studies showing that colonization of the upper airway by opportunistic pathogens, particularly Streptococcus, Moraxella and Haemophilus, is more common in asthmatics than in healthy subjects.

Protective bacteria

In addition, at the onset of an asthma attack, the relative abundance of Corynebacterium was inversely associated with the likelihood of severe exacerbation. It should be noted that Corynebacterium (the most abundant genus identified in nasal microbiota) less frequently prevails in the nasal microbiota of asthmatic adults, suggesting a protective effect, perhaps through competitive colonization. Corynebacterium and Dolosigranulum may indeed inhibit the growth of Streptococcus by releasing antibacterial substances.

Cause or consequence?

Therefore, the microbiota of the upper respiratory tract is linked to events that take place in the lower respiratory tract. However, the design of the study prevents from drawing any conclusion on causality relationship. It is not yet known whether changes in the microbiota I) give rise to asthmatic activity, II) are the consequence or cause of a viral infection, or III) are the result of a two-way dialogue between the microbiota and the immune response of the host at a mucosal level during attacks and exacerbation. Changes in the microbiota may also be due to poorer asthma control or an inflammation of the respiratory tract.