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Bacteria, dirt and stress — is a little less hygiene needed?

New research gives new weight to the so-called hygiene hypothesis, arguing that children, in the early years, need to be exposed to dirt (and by implication a diversity of bacteria) in order suggests to strengthen their immune system, and that such exposure increases the richness of the human microbiome — the collection of microbes that reside within the human body.

The hygiene hypothesis explains that the marked increase in autoimmune and inflammatory diseases since the 1950s is the direct result of changes in our exposure to microbes in childhood, which runs parallel to a reduced exposure to the less than sanitary conditions. The concept also relies on decreasing family sizes, such as having fewer siblings, which results in a reduced chance of exposure to pathogens. This remains theoretical, although the ideas are backed by a large number of scientists.

Some related research, within the broad hygiene field, has been undertaken at University of Colorado Boulder. Microbiologists and medics have been studying whether the reduced exposure to infectious agents is coincidental with an increase in inflammatory-related diseases. The effects of inflammation can lead to a higher risk of developing stress-related pathologies, like such as post-traumatic stress disorder (PTSD) and depression.

This has led to a consideration of whether stress-related disorders can be decreased (in terms of incidences or severity) by increasing a person’s exposure to environmental bacteria.

With this, lead researcher Dr. Christopher Lowry has told Bioscience Techniques: “Our approach wasn’t so much to modify the gut microbiome, but to protect the host from stress-induced microbiome changes.”

The work has involved looking at a soil bacterium called Mycobacterium vaccae. This bacterium has been linked to improved moods and lower levels of pain. To see if the bacteria can reduce stress, the research group vaccinated mice with a heat-killed preparation prior to exposing them to chronic social stress. It was observed that the bacterium did promote long-lasting and proactive coping behavior. In neurological terms, the organism could be exerting an effect on the serotonergic and microglia systems. This is, therefore, an area worthy of further exploration.

The research has been published in Proceedings of the National Academy of Sciences. The research paper is titled “Immunization with a heat-killed preparation of the environmental bacterium Mycobacterium vaccae promotes stress resilience in mice.”

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Dr. Tim Sandle is Digital Journal's Editor-at-Large for science news. Tim specializes in science, technology, environmental, business, and health journalism. He is additionally a practising microbiologist; and an author. He is also interested in history, politics and current affairs.

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