In a research study appearing in Cell, Harvard scientists have found that an individual’s microbiome is very species-specific and likely the result of a co-evolutionary process involving the host and its bacterial tenants. Bacteria are important for our survival and any disturbances to our “bacterial make-up” may be harmful to our health. I say our “bacterial make-up” because studies show that we are infested with bacteria and that there are 9-fold more bacteria than there are human cells in our bodies.
While it is well accepted that resident bacteria play an essential role in our optimal health, the current study looked to analyze whether our microbiome is custom made for each individual or whether any bacterial cohort will do.
In an attempt to answer this question, Dr. Dennis Kasper, Harvard Medical School professor of microbiology and immunobiology and his team bred mice that lack microbial flora and introduced microbial species that are natural to mice into one cohort of mice, and human microbes into the second cohort.
For both groups of mice, an equal quantity of microbes, and an equal diversity of species, soon flourished in their digestive tracts.
The team discovered that the mice with humanized microbes had low levels of immune cells which were equivalent to mice who lacked intestinal bacteria all together.
The experiment was repeated and a third group of mice were populated with microbes common to rats. Surprisingly, this new group showed the same immune system deficiency as the humanized mice.
In a third experiment, all groups of mice were infected with salmonella. Almost from day one, the mice with human flora showed significantly higher levels of salmonella in their system than the mice with normal flora. The immune systems of the mice with human flora were effectively incapable of fending off the pathogenic bacteria.
“This raises serious questions regarding our current overuse of antibiotics, as well as ultra-hygienic environments that many of us live in,” said Kasper. “If the bacteria within us is specific to us and necessary for normal immune system function, then it’s important to know if we are in fact losing these vital bacteria. Are we losing the bacteria we have coevolved with? If that is the case, then this is yet further evidence supporting the idea that the loss of good bacteria is partly to blame for the increased rates of autoimmunity that we are now seeing.”