Do Probiotics Colonise Your Gut?

Do probiotics colonise your gut? Or do they just pass through?

As many will know, our gut is home to a microbiome, trillions of bacteria from all sorts of different families, some of them permanent, some of them transient. The question is, when we take a probiotic, does that bacteria start to live in our gut permanently? Or does it just pass through? Well, there are a few factors that go into this to consider, so in this article we’ll talk about how long a probiotic can stay in your gut, what that means for you, and how that can impact its effectiveness.

How long do probiotics stay in your gut?

This really depends on a few things, but first, let’s just define the difference between some terms.

Colonisation is where a bacteria lives in your gut permanently. It reproduces, has carved out a niche for itself, and unless something major happens to affect its population, it’ll stay there.

Persistence on the other hand is accepting that a bacteria will not be in your gut forever, but is really more of a measure of how long it’ll stay present for, as eventually it’ll pass through.

The truth is, it’s extremely rare for a probiotic to colonise the gut in an adult microbiome. This is because the gut already has a lot of bacteria in it, and it’s very difficult for a new microbe to get established permanently and find an ecological niche.

But, this doesn’t mean that probiotics can’t help us out! The microbes we send in can still do great work for us and impact a variety of different processes within our bodies, and they can do this while they’re there, even if they are going to eventually transit out of the gut. And of course it goes without saying that the longer they stay in the gut, the longer they can help us, so good mucosal adhesion is a bonus.

How long they stay in the gut really depends on the strain of bacteria, and what it can do. Some have shown themselves to remain present for much longer than others, so let’s look at some of the things that can impact this.

Does probiotic strain matter?

The strain of bacteria is probably the single biggest influencing factor when we’re talking about how long a bacteria can stay in your gut.

Different strains of bacteria have very different surface proteins, and can therefore perform very differently. Aspects like their ability to adhere to the mucosal lining in the gut, the way they interact with the epithelial barrier, and even the degree to which they can compete with other bacteria, all play a part. All of these are different from strain to strain, even strains of the same family can behave completely differently. There have been many studies to show that two bacterial strains from the same family, so for example two varieties of Lactobacillus Rhamnosus, can stay in the gut for dramatically different periods of time. So, picking a good, proven strain such as LGG or BB12 can make all the difference.

How do probiotics stay in your gut?

The most common answer? Mucosal adhesion. Our gut has a mucous lining, and in a healthy person this lining can be quite thick. It’s often home to most of our gut microbiome and is teeming with trillions of microbes.

Some probiotic bacteria can adhere to this mucous, meaning that even though they will eventually pass out of the digestive system, they can stay present for a little longer than those that do not adhere. This can be a huge benefit for the person taking the probiotic as it means the good bacteria can stay present for longer, and therefore have a greater long term effect on their health.  

Let’s take LGG as an example.

One study compared LGG with another Lactobacillus rhamnosus, LC-705, to directly compare how well each of them adhered to the mucosal lining. Despite the fact that both these bacteria aren’t just from the same genus, but from the exact same species, they both demonstrated very different abilities to adhere to the mucosal lining. The LGG adhered very well, whereas the LC-705 adhered quite poorly and passed out of the digestive system very quickly, demonstrating that even though the bacteria might be from the same family, the degree to which they can remain in the gut varies between strains.

So, the upshot here is, strain matters! Some can stay present for days or even weeks, whilst others pass through the gut in hours, so making sure you’re taking a strain that has been proven to remain present in the gut for longer will help to ensure you can keep the population of your probiotic bacteria at a healthy level.

Do probiotics reproduce in the gut?

The short answer is, in some instances, yes. There have been many studies demonstrating that certain strains of bacteria taken as a probiotic can divide and multiply in the gut, or ‘reproduce’, helping to sustain their population.

However, it’s important to know that it’s exceptionally rare for these bacteria to divide at a fast enough rate to maintain their population, or even grow it, as they still ultimately pass through and out of the digestive system.

So whilst these bacteria can in fact reproduce, this really only extends how long they’ll be present in the gut, as they will still eventually transit through. The best way to overcome this is regular supplementation, adding more of the beneficial bacteria to make up for the ones that have passed out of the gut.

Do probiotics only work while you take them?

Since they all ultimately pass through, it’s not unreasonable to ask if probiotics can only really help us so long as we keep taking them. The answer however is actually that the positive effects of probiotics can sometimes subsist after supplementation stops.

For example, bacteria can interact with the mucosal lining in the gut, helping to rebuild it. If this happens, and the mucosal barrier is stronger as a result, then it might stay that way even if the bacteria that had that effect are no longer present.

Probiotics can also impact the surrounding microbiome of your gut. For example, if you took a strong probiotic to combat a population of bad bacteria, then once those pathogenic bacteria have been supressed you may find that you no longer need the probiotic, they’ve done their work, and a healthy diet is all that’s needed to keep your gut in shape.

However, this doesn’t mean probiotics are a quick fix. You still need to take a good probiotic for at least a month if not more to really start seeing the best results.

For long term gut support, it’s best to keep taking the same probiotic if you find one you like, as this helps to keep the microbiome consistent and resilient against any unusual bacteria that may be introduced. This can make a good alternative to eating fermented foods as a source of beneficial bacteria, as this was the traditional means of maintaining our microbiome. The idea in this is that because these bacteria can’t permanently colonise our guts, we keep adding them to keep that population strong, and keep receiving the benefits. It’s for this reason that most people use a probiotic in the long term.

Can probiotics colonise a baby’s gut?

Babies are slightly different. Their little guts are still developing their microbiomes, and there are considerably more ecological niches for new bacteria to grow in. Now, it’s unusual for a probiotic to permanently colonise a baby’s gut. But, research has shown that it’s not unusual for probiotics to last a lot longer in a baby’s digestive system before passing through. In some instances they have persisted for weeks and even months before passing out completely.

This goes some way to explaining how probiotic strains such as LGG and BB12 have been shown in paediatric research to help support gut issues in babies such as infant colic, as well as helping to mitigate issues that start in the gut, such as infant eczema.

Conclusion: Does better adhesion mean a better probiotic?

The simple answer is, not on its own, no. Adhesion is great in a bacterium that has been proven to have real health benefits, as it means that that good bacteria will hang around a lot longer, and have a positive impact for longer, which is always good news for you.

Ultimately though, the biggest deciding factor on how good a probiotic bacteria is really comes down to the clinical evidence. Any bacterium needs to have been proven to have positive effects for us to know it’s going to work, in real, high quality clinical trials. That’s the most important factor to remember. Good mucosal adhesion, such as that demonstrated by both LGG and BB12, is just an extra bonus for longer lasting effects, and in a bacterium with the level of clinical research that these two have, is a huge bonus. But good mucosal adhesion in a bacterium that’s never been proven to have any health benefits is much less of a help. Learn more about how to pick the best probiotic in our article here.  

References:

-              Tuomola EM, Ouwehand AC, Salminen SJ. Chemical, physical and enzymatic pre-treatments of probiotic lactobacilli alter their adhesion to human intestinal mucus glycoproteins. Int J Food Microbiol. 2000 Sep 15;60(1):75-81. doi: 10.1016/s0168-1605(00)00319-6. PMID: 11014524.