The gut microbiome may be involved in Kawasaki Syndrome

Clinical manifestations and time course of Kawasaki disease

Kawasaki disease occurs in young children, and is characterized by long-lasting fever, coughing, diarrhea, along with other symptoms. What specifically causes this disease is unknown, but scientists guess it may be influenced genetically or by intestinal microbiota. Japan seems to have an unusually high rate of occurrence of KD. Researchers in Tokyo performed a longitudinal study of the intestinal microbiomes of KD patients, in order to look for any patterns that could suggest a relationship between intestinal microbiota and Kawasaki disease. The results have been published by Frontiers in Microbiology.

Fecal samples were collected from 28 Japanese children, ages ranging from 3 months to 9 years 6 months. Patients were both male (15) and female (13).  Fecal samples were collected twice from each child, for a total of 56 samples. The first (acute phase) sample was taken at the time of hospital admission, while the second (non-acute phase) was collected 4-6 months after the onset of Kawasaki disease. DNA was extracted from the fecal samples and sequenced to determine the bacterial composition of the intestines.

Roseburia species were found to be relatively abundant during the non-acute phase (4-6 months after disease onset). Species of Streptococcus were found mainly during the acute phase, such as S. pneumonia, orlais, pseudopneumoniae, mitis, gordonii, and sanguinis. This means there is a potential that these species of Streptococcus could be related to KD. To further determine if the Streptococcus species were related to KD, the researchers compared the species’ genomes to recent research in which they are involved, and found that Streptococcus could be a biomarker or pathogen for diseases with unknown causes, such as Kawasaki disease. While this is still a hypothesis and nothing is proven to be 100% true yet, it is definitely a topic that will be researched extensively in the nearby future. It may hold the key for understanding many other diseases whose causes are a mystery.   

Infants’ saliva may react with breast milk to modulate their microbiomes

Breastmilk is critically important to developing a healthy infant gut microbiome.  The combination of oligosaccharides found in breastmilk are not found in any other individual food, and are intended to cultivate healthy bacteria in the gut.  Besides breast milk, really the only other fluid an infant consumes is his or her own saliva, but thus far not much is known about the role this saliva plays in culturing the proper microbiota.  A team of researchers from Australia recently studied how a mother’s breastmilk directly interacts with her infant’s saliva.  They discovered that when combined, saliva and breast milk produce specific molecules that inhibit the growth of some bacteria, but support the growth of others. They published their results in the journal PLoS ONE.

The researchers measured the molecular components of saliva in 77 adults and 60 infants.  They noticed some stark differences between the two types of saliva, including markedly higher levels of salivary hypoxanthine and xanthine.  Hypoxanthine and xanthine are both substrates for a protein called xanthine oxidase (XO), which reacts with them to form hydrogen peroxide (H2O2).  One of the places XO is predominantly found is in human breast milk, which led the researchers to hypothesize that xanthine and hypoxanthine in infant saliva reacts with XO in breastmilk to form H2O2.  Hydrogen peroxide is a reactive oxygen species (ROS) that can kill bacteria.  The scientists believe that infant saliva reacts with breast milk to form hydrogen peroxide at high enough levels to kill opportunistic pathogens, but allow others to grow.  In order to test their hypothesis, the researchers combined breast milk and infant saliva and attempted to culture the pathogen Staphylococcus aureus, along with gut commensal bacteria Lactobacillus plantarum, and Escherichia coli.  They found that the mixture created concentrations of hydrogen peroxide that killed the S. aureus but allowed the commensals to grow.

Overall this paper showed that infant saliva can combine with breast milk to form physiologically relevant concentrations of hydrogen peroxide.  The hydrogen peroxide may in fact select for the growth of specific bacteria in the mouth and gut, and lead to the development of a healthy microbiome.  Interestingly, pasteurized cow’s milk and infant formula did not contain XO, the enzyme necessary to create the hydrogen peroxide, adding another reason why there is no true substitute for breast milk.   

Interactions of microbiome, diet, and genetics modulate predispostion to diabetes and metabolic syndrome

The human population is undergoing epidemics of metabolic syndromes, type 2 diabetes, and cardiovascular disease and the reasons for these increases in prevalence are not entirely known.  Scientists understand that this rise may be a combination of genetic risk factors as well as environmental risk factors. Scientists from Harvard, Washington University in St. Louis, and the Helmholtz Center in Germany published a paper in Cell Metabolism investigating three strains of mice and analyzing interactions between host genetics, diet, and the gut microbiota.

They used two strains of mice from the Jackson Laboratory (B6J and 129J) and one strain from Taconic Farms (129T). They Taconic strain is very similar to the 129J strain from Jax however it is given a probiotic, resulting in a difference in its gut microbiome. They also inbred the three strains for several generations to create environmentally normalized mouse groups.

They found that the Taconic 129T mice were similar to the 129J mice in their development of diet induced obesity after a high-fat diet but they only developed mild glucose intolerance in comparison to the Jax mouse strain. After inbreeding these mice for three generations in the same environment, these differences were lost. After analysis including 16s sequencing, the original differences in phenotypes and the changes following inbreeding normalization were a result of microbiome differences and microbiome differences were largely dependent on diet, host genetics, and environmental history.  They also found strong strain-dependent and strain-independent relationships between specific phenotypes and bacterial communities that indicated strong interactions between the microbiome, diet, ancestry and genetics.

This study shows that metabolic syndrome and related conditions is the result of complex interactions between genetic and environmental factors, including the gut microbial community. These interactions between diet, genetics, and the microbiome present a significant challenge in the analysis of human disease. 

The oral microbiome of schizophrenics differs from controls

Self-portrait of Vincent van Gogh, who likely had schizophrenia

The gut-brain axis is a very intriguing field that offers a lot of promise in making progress in neurological diseases.  The science is still very new, though, so much work needs to be done in establishing any connections between the microbiome and these diseases.  The reason the gut is normally explored is because of the strong connection between the gut and the brain via the vagus nerve, which in initial studies has been shown to be an important pathway for afferent and efferent connections.  Other body microbiomes’ connections to the brain have not yet been studied.  A new study that came out last week makes a connection between the oral microbiome and schizophrenia, a disease which had previously been linked to the gut microbiome.  The results were published in the journal PeerJ.

The scientists performed whole genome sequencing on the oropharyngeal microbiomes of 16 people with schizophrenia and 16 healthy people.  Importantly, the scientists note that the people with schizophrenia were more likely to be smokers and to be overweight, two qualities that are already associated with alterations of the oral microbiome.  The results showed that the schizophrenics had lower overall diversity of their oral microbiomes compared to controls.  Specifically, lactic acid bacteria, and especially Lactobacillus gasseri, were more abundant in the mouths of those with schizophrenia, even after controlling for other variables such as age and smoking status.

While this paper does not attempt to explain why these differences occur, they are quite interesting nonetheless.  If somehow the disease state can be characterized by the oral microbiome this could be important for diagnostics.  The next step is to actually establish if any of the connections between the bacteria in the body (including the mouth) and the brain are partly responsible causing the disease.  If this is the case then not only would it help explain the environmental causes of schizophrenia, but it would also lend itself to possible microbiome treatments for the disease, such as pro- or pre-biotics.

New probe developed to detect specific bacteria associated with bacterial vaginosis

Confocal laser scanning images with 400x magnification of G.vaginalis biofilm in 2 vaginal slides (A and B) in a superimposed image: vaginal epithelial cells in blue and G. vaginalis specific PNA-probe in red. A: vaginal sample with dispersed bacteria; B: vaginal sample with bacteria in biofilm.

Bacterial vaginosis (BV) is a topic we have previously covered on the blog, because of its significance to women’s health. BV is a change in women’s vaginal bacterial composition, in which bacteria that are usually associated with health are at a decreased presence in comparison to BV-associated bacteria. BV is such an issue because it causes a biofilm to form that increase susceptibility HIV and other sexually transmitted infections. BV also has negative effects on pregnancy and is a threat to women of reproductive age. Clearly this is an important topic of research, and was the focus of an article recently published by PLOS ONE.

BV is usually characterized by the presence of Gardnerella vaginalis and Atopobium vaginae. A.vaginae has previously been shown to be much more common than G. vaginalis in BV patients. In the PLOS ONE study, researchers focused on finding the best way to detect these two bacteria in vaginal samples. Samples were taken from 119 women in Rwanda, between the ages of 18 and 35 years old. After testing multiple different probes that had been developed by the researchers, they found that something called the PNA FISH is a very good tool for detecting bacteria in biofilms. Through this study the scientists were able to detect that higher quantities of G. vaginalis and A. vaginae are associated with bacterial biofilms. Almost half the samples containing G. vaginalis also contained A. vaginae, whereas all of the samples that contained A. vaginae were also positive for G. vaginalis.

With the data collected, the researchers hypothesize that G. vaginalis is a main cause of vaginal biofilms when it is high enough in concentration. Hopefully with the discovery of effective probes, much more can be discovered about bacterial vaginosis.    

Different types of dietary fat affect obesity through changes to the microbiome

A triglyceride molecule, the main constituent of lard.

Dietary fat comes in many in many different forms, such as saturated fats that come from foods like lard, and polyunsaturated fats that come from foods like fish oil.  It is generally believed that saturated fats lead to inflammation and obesity, but that polyunsaturated fats are healthier, and can counteract inflammation and promote healthy metabolism.  The role of the microbiome in mediating these effects is still unknown, but is beginning to be elucidated.  A team of researchers from Sweden, Belgium and Denmark showed that the lipids themselves alter the microbiome, which induces the characteristic inflammation associated with ingesting saturated fats.  Their results were published in the journal Cell Metabolism.

The scientists fed groups of mice identical diets that only differed in the type of fat that was consumed: lard composed of saturated fats, and fish oil composed of polyunsaturated fat.  As expected, the group that ate the saturated fat gained weight and had higher fasting glucose than those eating unsaturated fat.  When they measured the gut microbiomes of these mice, they discovered that the overall diversity of bacteria were much lower in the mice eating the saturated fat diet.  Next, the scientists measured the contents of the blood of the mice and discovered that there were higher levels of bacterial metabolites and bacterial components in the blood of mice eating the saturated fat diet.  Using complicated techniques that are beyond the scope of this blog, the researchers were able to trace the inflammation to an increase in specific receptors in the gut that are activated by bacteria from the saturated fat diet, including some specific toll like receptors (TLRs).  The scientists conducted a final experiment to show the importance of the microbiota, rather than the diet, in inducing these effects.  They transplanted the feces of both groups of mice into new, healthy mice.  The mice given the feces of the saturated fat group gained weight, whereas the ones given the microbiomes of the polyunsaturated fat group tended to lose weight.

The scientists believe that diets high in saturated fats upregulate specific immune system receptors that are activated by factors derived from the gut microbiome.  Moreover, these factors find their way into the blood much more easily after consuming saturated fat, as opposed to unsaturated fat, so they can easily activate these receptors.  After activation the factors lead to inflammation and obesity.  Overall, this research explains one of the reasons why polyunsaturated fats are healthier than saturated ones.  We know It’s not often anyone is faced with the choice between fish and lard, but after reading this study we recommend our readers go with the fish.