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New Animal Research Points to the Connection between Bacteria and Disease

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What causes disease? The answers are manifold, but recent mouse studies point to a new culprit in certain diseases: bacteria.

Gut Bacteria & Brain Health

In a study with mice, researchers at Washington University in St. Louis and the University of Chicago discovered a link between gut bacteria and brain health and found that changes to the microbiome could worsen the cognitive decline associated with neurodegenerative conditions such as Alzheimer’s disease.

Recent research has already uncovered links between Alzheimer’s and an altered gut microbiome, but so far there has been no clear determination as to whether this is a cause or an effect of the disease.

The researchers fed mouse models of Alzheimer’s antibiotics for a week, which caused permanent changes in their gut microbiome, immune responses, and cognitive impairment related to the development of tau protein.

The discovery could lead to new ways to address neurodegenerative disorders by manipulating the gut microbiome.

Bacteria & IBD

A team of scientists at the Wellcome Sanger Institute, the Hudson Institute for Medical Research, and the University of Cambridge, have discovered two new strains of bacteria in the microbiome of mice that cause Inflammatory Bowel Disease (IBD), a lifelong condition caused by chronic inflammation of the gastrointestinal tract.

The exact cause of IBD is unknown, but it is thought that the immune systems of people with IBD may be reacting to normal bacteria in the gut. In an attempt to get closer to finding a cause, the researchers studied the microbiomes of 600 mouse models of IBD and identified two new bacteria that were causing IBD symptoms in the mice, including weight loss and intestinal inflammation.

Accounting for the presence of these two bacteria—called Duncaniella muricolitica and Alistipes okayasuensis—could improve research outcomes in future studies on IBD.

Lupus-Causing Bacteria

There is no identified cause for lupus, a condition in which the immune system attacks the body. Lupus does have a genetic component that makes certain people more susceptible to it, and the gut microbiome is known to play a role in the manifestation of symptoms, but the trigger for the disease is unknown.

Now, researchers at Tohoku University School of Medicine in Japan have connected skin microbes with lupus. The team used a mouse model of Sjögren syndrome, an autoimmune disease that is also present in approximately 20% of lupus patients with systemic lupus erythematosus (SLE), a more severe type of lupus.

The Sjögren mice were found to have an excess of Staphylococcus aureus bacteria compared to normal mice, and their skin cells produced less of the mRNA needed to fight infection. When the Sjögren mice were treated with antibiotics for that bacteria, they showed less severe autoimmune symptoms, indicating that there may be a connection between the bacteria and the disease.

After applying more of the bacteria to the skin of the mice, the team observed that the mice not only experienced more inflammation and increased autoimmune symptoms, they also developed renal failure, which is common in cases of SLE.

The team hopes to be able to move to clinical trials to develop ways to alleviate severe symptoms in lupus patients.

Nose-Picking and Dementia

A team of researchers in Australia and the UK has found that the bacteria Chlamydia pneumoniae, which is found in the respiratory tract but can also infect the central nervous system, can increase the risk of contracting Alzheimer’s and other forms of dementia.

Previous research has already shown the bacteria to be present in the brains of Alzheimer’s patients, but the team wanted to discover how it got there. To find out, they injected the bacteria into the noses of a group of mice. Control mice received a dose of saline solution.

Studying the brains of the mice, the team discovered an elevated level of Chlamydia pneumoniae bacteria located close to their noses, surrounded by clusters of beta-amyloid—a protein that is a hallmark of Alzheimer’s disease. The control mice also had beta-amyloid protein in their brains but in lower, less concentrated levels.

So, what does this have to do with nose-picking? The researchers cautioned that nose-picking can damage the lining of the nose, allowing Chlamydia pneumoniae to more easily travel to the brain.

Does Bacteria Cause Rheumatoid Arthritis?

Rheumatoid arthritis is an autoimmune condition that causes joint inflammation, pain, and swelling. The antibodies that cause rheumatoid arthritis have been known to form in specific areas of the body—including the mouth, lungs, and gut—before symptoms appear, and new research from the University of Colorado may have uncovered why.

Investigation uncovered a previously unknown bacteria species that is not present in the intestines of healthy people but is found in the intestines of approximately 20% of people who have rheumatoid arthritis or the antibodies that cause it.

This new species, which the researchers named Subdoligranulum didolesgii, could be triggering an immune response, but rather than attacking the bacteria, the antibodies attack the joints.

The next step is to determine how widespread the bacteria is in the general public, and whether it directly causes rheumatoid arthritis.

Cancer-Fighting Bacteria

In some cases, bacteria work not to cause disease, but to prevent it. Scientists at Stanford University have discovered a way to harness some of the microbes living in and on our bodies and transform them into little cancer-fighting machines.

The researchers chose to use Staphylococcus epidermidis, a relatively harmless microbe commonly found on human skin. The team then inserted a new gene into the microbe that would allow it to recognize some cancer cells.

They applied the modified microbes to the skin of mice, then injected the mice with skin cancer cells. A different group of mice was given the unaltered microbe and also injected with skin cancer cells. As the cancer cells grew into tumors, the researchers observed that the cancer was much slower growing in the mice with the engineered microbe.

There are still many details to work out, including which microbe should be used and what type of cancer to target but the team hopes to begin human trials within a few years.

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