If you were to take a microscope to your intestines, you would see tens of trillions of microbes moving around doing what they do best: eating and multiplying. Yet, while this may appear to be a utopic environment, what's happening is exactly the opposite. There's a microbial war happening and your health depends on which side wins.
There are hundreds of microbial species living inside each of us and each of us is unique in our microbial makeup. Yet, we can group inhabitants into one of three categories. Commensals are essentially bystanders, which increase the diversity of the environment. Then there are the symbionts, our friends, which provide us some benefit. Finally, there are the pathobionts, which as the name implies, are for the most part, foes. These species antagonize us and promote a state of inflammation, which over the long term can have overall health consequences.
Most of the research into these three categories has not surprisingly focused on their interactions with our bodies. We've gained insight into the various mechanisms bacteria use to communicate with us using chemical signals. As a result, we have a clearer understanding of how certain species can influence our overall health. The overall message from this collection of studies is rather simple: keep your friends close and eschew your foes.
But the human-microbe interaction represents only a fraction of what is happening on the inside. The microbes are also interacting with themselves. It turns out many are rather discriminating in their choice of friends. When they come across species they like, a harmony can be formed. But, if the neighbour is antagonistic, some microbes are less than tolerant. Thankfully, when it comes to war, our friends are much mightier than our foes.
One of the hallmarks of friendly bacterial intolerance is a chemical known as a bacteriocin. It's produced by a number of bacteria, many of which we consider to be friends. Not surprisingly, these bacteriocins are also produced by several probiotic species, such as Lactobacillus acidophilus. When billions are introduced into the mix, they can begin to look for and attack foes. Over time, addition of these bacteriocin-producing bacteria, such as Lactobacillus casei, can change the overall makeup of the population. By adding these species to the gut, one can improve the ratio or friends to foes and possibly improve health.
In addition to probiotics, other species in the gut may also act as friends by keeping those foes from causing trouble. Last week, an American team of researchers revealed one particular commensal bacterium also appears to be capable of driving away pathobionts. The name is Bacteroides fragilis and based on the findings, it's presence means bad times ahead for pathobionts.
B. fragilis has the capability of delivering a toxic blow to unwelcome visitors using a technique called the Type VI secretion system, or T6SS. While the name may seem cryptic, the mechanism is rather straightforward. The bacterium comes into contact with the victim and then creates a tunnel between the two cells. Once the link has been formed, toxins are sent into the target cell. The process is essentially death by injection and it is incredibly effective.
At first, experiments were done in bacterial cultures to ensure B. fragilis could kill other species. Once that was determined, the experiment was conducted in mice raised with a specific gut microbial population. If the researchers were correct, the population would be different in mice fed the bacterium compared to those going without. As expected, the addition of B fragilis had an effect as the populations inside test mice changed. Several foes were targeted and their concentrations were reduced.
Once the experiments were completed, the team was able to examine how B fragilis might work in the human body. They developed mathematical models and tried to estimate how influential this mode of foe control was in overall health. They calculated this species could have anywhere from 60 to 600 billion interactions per day and over time could change the overall diversity towards a more friendly population.
There is a catch. While the number of interactions and possible kills may seem significant, this activity only affects less than 1% of the tens of trillions of bacteria in the gut. Moreover, the actual effect is short term, not permanent. Regular supplementation would be needed to keep the population stable.
At the moment, you cannot get B fragilis on the store shelves as it's considered a commensal or bystander rather than a probiotic friend. But you do have it inside you and can help keep it active by giving it food it loves, complex plant polysaccharides, also known as fibre. By keeping up this routine, you can help ensure the inevitable microbial war on the inside is at least skewed towards your benefit.
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