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Our intestines are home to trillions of gut bacteria with a combined weight of approximately one kilogram. The interaction between our intestines and these bacteria alternates between love and war. Most of these micro-organisms are important to our health, which is why we take good care of them. Sometimes, however, pathogenic intruders show up and disrupt the balance; while at other times our intestines fail to handle the ‘good’ bacteria as they should. Infection biologist Karin Strijbis researches the fascinating ways our bodies deal with the bacteria present in our intestines.
 

‘The composition of the bacteria present in a person's intestines is determined during the first four years of their life,’ Strijbis explains. ‘It begins during birth. Is it a vaginal birth or a Caesarean section? This decides which bacteria settle in the intestines first. After that, factors such as nutrition – breast milk or formula – play an important role in rounding out the population of bacteria in the intestines, the so-called gut microbiome.’ When their numbers are complete, trillions of bacteria live in our intestines, with some 100 to 200 species present. All together, these bacteria weigh around one kilogram.

mucous layer with a dual function

Strijbis is conducting research aimed at the mucous layer in our intestines. ‘That mucous layer is comparable to the more familiar mucous layer inside your nose. The layer has a dual function. It ensures that “good” bacteria are able to survive and is the first line of defence against “bad” micro-organisms such as viruses, fungi and bacteria.’ While your mouth, nose, throat, lungs, stomach and intestines are all lined with this type of mucous layer, little is known about the mucous layer in the intestines.
 

In the Netherlands, these diseases affect one in 200 people

Gut problems

First, a word about those ‘good’ bacteria that are so vital to our health. ‘They help us digest food, produce essential vitamins and even have an effect on our brains and auto-immune diseases. They're incredibly important, in other words, but unfortunately the system doesn't work properly for everyone. Some people are prone to intestinal inflammation, which is a problem the majority of the population never experiences. Other people are affected by intestinal disorders such as Crohn's disease and chronic bowel inflammation. In the Netherlands, these diseases affect one in 200 people. To help them, we must gain a better understanding of how the mucous layer works and how the various species of bacteria affect our bodies. This is what I'm trying to find out, in order to contribute to prevention and facilitate treatment for people with gut problems.’

Promising proteins

Last year, Strijbis was awarded a European Research Council Starting Grant, which provides young researchers with €1.5 million in funding to establish their own research group. Strijbis has since used the grant money to hire three researchers. ‘Our research focuses mainly on specific proteins found in the intestinal mucous layer. These proteins acts as detectors. When a pathogenic bacterium turns up, these proteins are able to repel the bacteria and send a warning signal to the body.’
 

‘There is an ongoing battle between our immune system and pathogenic bacteria’

Ongoing battle

A darker side to the story is revealed when Strijbis begins to talk about the ‘bad’ bacteria. ‘Our bodies are locked in an eternal war with dangerous intruders. Together with our immune system, the mucous layer is fighting a constant battle against pathogenic bacteria that gain entry to the body via things like raw foods and surface water.’ Campylobacter and Salmonella are examples of such bacteria. In addition to the ongoing battle, there is also a continuous arms race in effect, Strijbis explains. ‘Bacteria are finding new methods of infecting people and we humans keep generating new responses to slow or prevent those infections. While research into gut bacteria and the mucous layer may not be considered a sexy topic, I find it utterly fascinating.’

Intestinal health in animals

While Strijbis’ research primarily concerns intestinal health in humans, she recently began collaborating with pharmaceutical manufacturer MSD to research intestinal health in animals as well.

By comparing human intestines to those of animals, Strijbis hopes to take her research to the next level. ‘Every species of animals – including humans – has a mucous layer with distinct characteristics. It is therefore likely that different species’ guts will react differently to intruders. We know, for instance, that chickens are not negatively affected by Salmonella bacteria, but that it can cause a serious bowel infection in humans. If we can figure out the source of such differences, it might offer clues to developing new treatments. And of course, we're conducting this research on different animal species with the “One Health” objective in mind, which is to improve the health of people, animals and the environment. We are attempting to determine which diseases can make the jump from animals to people, and what adaptations they need in order to do so. Did I mention how utterly fascinating our field is?’ 
 

This is an article from Vetscience no. 8, July 2020.