Could Bifidobacteria Assist the Brain in Behavior and Development?

Student Summary by Olivia Liu

Original Source: Berkley Luk,  et al., PLOS ONE, May 15, 2018 https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0196510

Image created by Olivia Liu

Abstract

Background: Our body is a residence to trillions of bacteria, which start making themselves at home the minute we're born. Most bacteria in the body are probiotic/commensal bacteria, or in other words "good bacteria." Some bacteria that are categorized in this section are bacteria in the gut. These bacteria play a role in developing the Central Nervous System (the CNS consists of the brain and spinal cord).

Objective/Hypothesis: It was hypothesized that having the right types of gut bacteria, such as bifidobacteria, could impact how the brain and nervous system develop and how our behavior changes in later life.

Method: In order to test the hypothesis, Berkley Luk and his team compared behaviors of three different types of mice: 1.) Germ-free mice (the control) 2.) Germ-free mice with human bifidobacteria 3.) Germ-free mice with normal gut bacteria. Both male and female mice in each of the groups were looked after in sterile isolated cages for around 7 weeks from when they were born. After those 7 weeks, the mice's anxiety levels, levels of activity, motor performance and coordination, memory, and social behavior were examined through several different experiments.

Results: The result showed that the mice with the normal gut bacteria had the greatest diversity of microbes in their gut; the bifidobacteria were the most abundant in the gut of the human bifidobacteria-treated mice; and the germ-free mice gained other species of bacteria from their different environments. On top of that, the experiments had shown several different behaviors: 1.) The female mice that had only the bifidobacteria were shown to have normal levels of anxiety. 2.) Germ-free female mice were hyperactive. Colonization with bifidobacteria did not fix this in the females — only the normal gut bacteria did. In the males, bifidobacteria actually lowered activity. 3.) When treated with bifidobacteria early on, the male mice had performed better than the germ-free mice in motor performance. 4.) Only germ-free mice had poor memory compared to the bifidobacteria-treated mice and the mice with the normal gut microbes (didn't matter what sex they were). 5.) The female mice that were treated with the normal gut microbes were found to be social; however, the germ-free and bifidobacteria-treated females were not sociable.

Conclusion: In conclusion, this study showed that putting bifidobacteria into the gut improved some performances on the behavioral tests. Maybe some parts of the brain were more sensitive to change because of these bacteria compared to others. This information could be useful in the future in order to better understand how microbes and their host interact with each other.