Analyzing bacterial adhesion in the gut to strengthen the health-promoting properties of probiotics
Malin Edvardsson Jan 25, ’22 ~ 14 min

Analyzing bacterial adhesion in the gut to strengthen the health-promoting properties of probiotics

Recently, there has been a lot of discussion on the microbiome, the gut-brain axis, and what impact the gut microbiota has on several aspects of our wellbeing. Curious to learn more, we talked to Dr. Joana Ortega-Anaya, postdoc researcher at the Department of Food Science and technology, at the Ohio State University. We talked about the complexity of the microbiome, how probiotics work, and Dr. Ortega-Anaya’s research on how to make a better probiotic.

What is the microbiome?

The microbiome is referred to as a group of microorganisms in a certain environment, for example in an organ, in a small animal, or in a plant, Dr. Ortega-Anaya explains. It is a specific and characteristic collection of microbes. In humans, we have a few microbiomes that are very important. We have the skin microbiome, i.e., the skin collection of microbes. Then we have the oral microbiome, in the mouth, and we have the respiratory microbiome, in the nose, lungs, and respiratory system. We also have the urogenital microbiome, and the most important one, that has been receiving a lot of attention lately, is the gastrointestinal microbiome, also called the gut microbiome, Dr. Ortega-Anaya says.

The gut-microbiome has a direct impact on our health

The gut microbiome spans from the stomach to the intestines, and it is very important because the intestines are connected to the bloodstream. I.e., what happens in the gut has a direct impact on our health, because whatever happens in the gut gets transported to blood vessels and organs, Dr. Ortega-Anaya says. So, there is a connection between what happens in the gut and what happens in our organs. The gut microbiome is what I am interested in, and this is where I focus my research, she says

The gut microbiome is affected by many, many factors. It is a very complex environment, and it is not a one-way street, it is a two-way street. In general, it is affected by where we were born, where we live, the geological Geographical location of our bodies, of course, the diet, if we are feeling sick, if we have a disease, and so on, Dr. Ortega-Anaya explains.

Listen to Pod Episode: The microbiome, probiotics and research on bacterial  adhesion in the gut

The equilibrium of the symbiotic and pathogenic microbes can change

The microbiome in your gut consists of a certain amount of pathogens, and a certain amount of non-pathogens, i.e., beneficial bacteria, Dr. Ortega-Anaya says. This population has a specific equilibrium, so when something happens, for example, if you get sick, or if you are stressed, that equilibrium gets modified. It might be that some pathogens proliferate, and the non-pathogenic bacteria are not proliferating as they should, and this results in a modification of such equilibrium. As a consequence, you can have specific alterations in your health that can go from just feeling a little sick in your tummy to having colitis or infections, diarrhea, and from then on; it can even evolve to cancer. But it is very complex. There’s not one little point or one little thing that you can say “If I do this, I am not going to get this disease”. It’s very complex, because bacteria are also very complex, as well as their interaction in the intestinal cells, Dr. Ortega-Anaya says.

Promote the good microbes to strengthen the gut-brain axis

What you can do to increase the chances of wellbeing is to support the good bacteria by doing more of what is beneficial for them and do less of what would promote the bad bacteria, Dr. Ortega-Anaya says. Two key activities that support the good microbes are a good diet and exercise. This also affects the so-called gut-brain axis, which is the connection between your gut and the health of your brain. The gut-brain axis is largely dependent on the microbiome. So, if your balance is not in optimum condition, then your mental wellbeing probably could be in a better state. And vice versa, if you get stressed, if you have a certain mental condition or a mental disease, that also affects the microbiome. So, it goes both ways, Dr. Ortega-Anaya says.

Using probiotics to support the microbiome

When we have an unbalance in our microbiome, we can ingest good bacteria to help us change this towards a desired optimal state. Such good bacteria are called probiotics and could, in fact, be bacteria or yeast. The World Health Organization (WHO) defines probiotics as “live organisms that when ingested provide a beneficial effect to the host”. In general, there is probiotics for the skin, for animals, and of course for the human gut, Dr. Ortega-Anaya says.

The probiotic label is dependent on the strain. We cannot generalize a group of bacteria. Usually, if we think about the Lactobacillus genus, we think of probiotics but it’s a fact that not all Lactobacillus are probiotics and not all probiotics are lactobacillus. There is different genus of gut probiotics, like Bifidobacterium, Enterococcus, and Streptococcus, but the specific strain, or the species of that bacteria, differs. I.e., one strain of the same lactobacillus can be probiotic and the other cannot as is the case of gut probiotic Lactobacillus rhamnosus vs Lactobacillus jensenii, which has a probiotic effect in the vaginal tract but not in the gut.

The probiotic mechanism differs between bacterial strains

There is a list published by the WHO regarding the bacteria that are considered probiotics up to this date, but that list changes as they perform new analysis, Dr. Ortega-Anaya says. The mechanism that the bacteria use to be probiotic is different in each of the strains and hence, it's hard to characterize. This makes it a very complex subject and it is difficult to predict which strains are probiotic, and which are not. One mechanism could be through the generation of bacteriocins which are molecules that prevent pathogens from growing; another mechanism could be to secrete proteins that help the gut barrier function, as well as those cells that line the intestines, or it could be something different. This is currently not perfectly characterized yet, Dr. Ortega-Anaya says.

A probiotic needs to endure the gastric conditions and to adhere in the intestine

For a probiotic to be considered probiotic, the first thing that it needs to do is endure the gastric conditions, i.e., the low pH, the bile salts, etc. Once it does reach the duodenum, which is the first part of the intestine, what it needs to do at that point is to adhere to the intestinal mucosa. The adherence is pivotal for the bacteria to be considered a probiotic. This is because all the microbiome is on such mucosa, and that’s where everything happens, Dr. Ortega-Anaya explains. All gut bacteria adhere to the intestinal mucosa. So, when you ingest a probiotic, the first thing that it does once it enters the intestine is to adhere to the intestinal mucosa.

Verifying bacterial adhesion to the intestinal mucosa

So how can you tell if the bacteria is adhering to the mucosa? There are many biochemical tests that allow you to verify the bacterial adhesion, for example, you can test the hydrophobicity and you can do cell culture experiments and measure if they bind, Dr. Ortega-Anaya explains. Some cultures are very expensive, and not everyone has a cell culture facility in their lab. Typically, they then do a biochemical test, which does not really mimic what is happening in the intestine. Therefore, my approach was to test the adherence using QCM-D, she says. I also wanted to explore the probiotic phenomenon, where the more adherence a probiotic has, the longer the residence time is in the mucosa. And longer residence time means that it will be able to exert the probiotic effect by whichever mechanism it does, she says. I wanted to test four strains of probiotic bacteria of Lactobacillus using QCM-D, where my main goal was to make a better probiotic.

Making a better probiotic

So how do you make a better probiotic? I work with dairy, dairy science, dairy chemistry, and everything dairy, Dr. Ortega-Anaya says. Specifically, we work with something called the milk fat globule membrane. This is a tri-layer membrane composed of phospholipids and membrane-bound proteins. This membrane surrounds the fat globules during lactation. It is synthesized by the mammalian gland cells during lactation, and then once the milk is secreted, each one of the fat globules has this membrane. However, there is a lot we don’t know about the milk fat globule membrane and its impact on human health, Dr. Ortega-Anaya says.

There are two groups of molecules that form the milk fat globule membrane, and I was interested in testing the phospholipids because they have been proven to modify the microbiome of pup rats, she says. The phospholipids have been observed to have a positive effect on the intestinal cells, preventing inflammation and enhancing the intestinal environment. Typically, such experiments are made on animal models, or on cell culture using Caco-2 cells which are intestinal cells, but they don’t produce mucosa. This means that these experiments need an extra step where you would be able to see if the bacteria bind to the mucosa, she says.

In my research, I use a co-culture comprised of Caco-2 cells, i.e., epithelial intestinal cells, and goblet cells, Dr. Ortega-Anaya says. Goblet cells are naturally found in our intestines, and those produce mucosa, so there, we have a better intestinal model. What I wanted to do was to take phospholipids from the milk fat globule membrane, and give them to the probiotic bacteria, i.e., the Lactobacillus bacteria; and make them adapt to have the phospholipids available while they grow, she says. We used four strains of Lactobacillus that are available in dairy and other food products: Lactobacillus acidophilus, Lactobacillus casei, Lactobacillus delbrueckii, and Lactobacillus plantarum. The bacteria of the four strains were fed milk phospholipids to study the effect that this would have on the bacterial adhesion and on the bacterial membrane morphology. I wanted to see if I could detect any changes and in fact, I did observe a significantly improved adherence to the intestinal model for some of the strains, Dr. Ortega-Anaya concludes.

Science on surfaces

Listen to the full interview with Dr. Joana Ortega-Anaya, to learn more about her research using QCM-D analysis to characterize bacterial adhesion in the gut and to strengthen the health-promoting properties of probiotics.

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