Whatever you do throughout your day, you are constantly bringing microbes onto and into your body. Especially when eating, you introduce a mix of microbes into your gastrointestinal tract.

In this dark, airless place, microbes flourish, working tirelessly to keep you in good shape. They improve your body’s health starting from the gut and strengthen your gut’s defences by fighting off unwelcome intruders.

Gut bacteria break down the food you eat from which they produce all sorts of molecules. The most important ones are called short-chain fatty acids. These small molecules impact the health of your gut and your overall body.

Here, we’re looking at gut bacteria that produce short-chain fatty acids and how they maintain the health of your gut. We’ll also explore ways to help bacteria make even more of these beneficial molecules.

Let’s start by understanding how your gut protects your body.

The mucus layer of the gut as a first line of defence

The food you eat passes through your body, yet it is always in contact with your body’s outer layer of cells. Only in the gastrointestinal tract do your gut cells absorb molecules from food and transport them into the body.

This means the outer layer of your gut, the so-called epithelium, faces away from the body and is in constant contact with the outside. One of its main jobs is to prevent harmful components from getting too close or even entering the body.

That is why goblet cells, which are special gut epithelial cells, produce a thick, slimy mucus. As they constantly secrete mucus, the cells actively push everything away from the epithelium, while the ever-growing mucus layer sits like a protective shield on top of the the intestinal epithelium.

When the mucus layer is too thin or broken, harmful microbes and bacteria can come into contact with the gut. This can trigger inflammatory immune responses, resulting in chronic diseases such as inflammatory bowel diseases.

Commensal gut bacteria produce short-chain fatty acids

While this slimy physical barrier is already a strong first line of defence for your gut, you can also rely on your gut microbes. Those that reside in and on your body over a long time are called commensal microbes.

One way to make them stay with you is by feeding them their favourite foods. Gut bacteria eat what you eat, while some commensals like Ruminococcus gnavus and Akkermansia muciniphila also eat the mucus in your gut.

And from your food, the majority of gut commensals prefer the dietary fibre. That is the indigestible part of plant-based foods as it passes through your small intestine unchanged. Once it reaches the large intestine, your gut bacteria get to work.

They break down the fibre, ferment it and produce all sorts of molecules from it. The most important group of molecules are the short-chain fatty acids, including acetate, propionate and butyrate.

The commensals Bacteroides thetaiotaomicron, Bifidobacterium longum, Eubacterium and Blautia coccoides are actually some of the best-known producers of short-chain fatty acids. Just by eating a lot of dietary fibre, you increase both the different microbial strains growing in your gut and the amount of short-chain fatty acids they make.

How short-chain fatty acids improve gut health

From the gut, short-chain fatty acids diffuse through the mucus and reach the epithelial layer. Here, they bind to receptors on the goblet cells and activate certain pathways.

They trigger goblet cells to grow and produce more mucus. This increasing mucus layer, in turn, protects more effectively against harmful bacteria while providing more food for your commensals.

For example, two gut bacteria, Akkermansia muciniphila and Blautia coccoides, produce the short-chain fatty acids acetate and propionate. Both molecules trigger gut cells to make more mucus, improving gut health and feeding commensal bacteria while fighting off intruders. In mice, Bifidobacterium longum induces the growth of mucus, likely by producing acetate.

The diet-microbiome-gut health connection

Now, let’s tie all these pieces together: By eating plant-based fibres, you feed your beneficial gut bacteria. These digest and ferment the fibre and produce short-chain fatty acids, which bind to your gut cells and trigger them to produce more mucus. This increasing mucus layer shields off your gut while feeding your gut bacteria.

Generally, the more fibre we eat, the more beneficial bacteria live in our guts. They become more active at digesting fibre since they lose their appetite for the mucus.

Beneficial bacteria like Blautia can even be found in human stool after 12 weeks of eating high-fibre diets. Hence, it seems that the commensal Blautia decides to settle down in your gut depending on what you eat. So, by eating food full of fibre, you can attract helpful bacteria to you.

On the other hand, when you eat little fibre, your gut bacteria start eating your mucus layer, since their preferred substrate is not available. This can lead to inflammation and other gut health issues.

You are what you and your bacteria eat

When considering the role of your gut bacteria for your health, the saying “you are what you eat” may take on a new meaning.

By eating a lot of different plant fibres, you’re not just feeding yourself — you’re also feeding the bacteria in your gut. Your food gives them the right fuel to produce short-chain fatty acids that strengthen your gut’s protective layer and gut health. This, in turn, impacts the health of your body, mind and cardiovascular system and even your emotional and mental wellbeing.

Hence, by eating more veggies, fruits and seeds with lots of fibre, you influence which types of bacteria live close to and inside of you. So, what you eat affects how you feel, quite literally from the inside out.

Your gut bacteria will thank you for that extra serving of vegetables. To show their gratitude, they’ll provide you with all the good stuff to keep you healthy.

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Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world

The complement system is the first line of immunity defence

As part of the innate immunity, the so-called complement system consists of several proteins. These get activated sequentially and function together to finally destroy any pathogen.

To recognise harmful bacteria, complement proteins have special receptors. These bind to specific proteins on the surface of the bacteria, so-called pathogen-associated molecular patterns, or PAMPs for short.

Imagine the bacterial PAMP as a key that perfectly fits into the groove of an immune receptor lock. The binding between these two proteins activates the immune system and triggers mechanisms that aim to clear out the pathogen.

The enzymatic lock & key hypothesis.

The immune system recognising different bacteria

Bacteria come in two main types: Gram-positive and Gram-negative bacteria. Depending on which type a bacterium is, it has different PAMPs. Luckily, your immune system has evolved to identify both of these structures.

Gram-positive bacteria are surrounded by a rigid layer, the so-called peptidoglycan cell wall. Within this layer of carbohydrates and proteins are the modified carbohydrates teichoic acid and lipoteichoic acid. These are the PAMPs, that your immune system recognises and binds to.

The Gram-positive bacterial cell surface. Created with BioRender.com.

On the other hand, Gram-negative bacteria contain an additional capsule layer on top of the peptidoglycan wall. This layer is made up of another type of carbohydrate, the lipopolysaccharide, which is the PAMP of Gram-negative bacteria. So, even though Gram-negative bacteria also contain a peptidoglycan cell wall, it is covered by the capsule and thus inaccessible to the immune system.

The Gram-negative bacterial cell surface. Created with BioRender.com.

How does the complement system work

Imagine a harmful bacterium managed to sneak into your body. To prevent any intruder from causing damage, the sensor proteins of the complement system are constantly patrolling the bloodstream, hunting for malicious beings that aim to harm the body.

As soon as a sensor protein recognises and binds to a bacterial PAMP with its lock, it alerts the complement system. The sensor protein begins to produce a key enzyme called C3 convertase.

A complement sensor protein binds to a bacterial PAMP. Created with BioRender.com.

Within your blood, there are lots of small complements called C3. And the main function of the C3 convertase is to break down this C3 into small C3a and large C3b fragments. This is the most important step in complement activation and from here everything else happens.

C3 convertase production and its subsequent action. Created with BioRender.com.

Now, the bloodstream is flooded with C3b fragments which bind to the bacterium’s surface. As more C3 proteins are broken down, more C3b large fragments are produced and more bind and coat the bacterium. This process is called opsonisation.

Illustration of opsonisation by C3b. Created with BioRender.com.

The immune system gets rid of bacterial intruders

The C3b-covered bacterium now acts as a location device for phagocytes. These arrive and bind to the C3b fragment very tightly. This keeps the bacterium locked and prevents it from moving around.

Now begins the process of phagocytosis, whereby arm-like structures extend around the bacterium, eventually engulfing, ingesting and destroying it. The infection is finally cleared.

Phagocytosis of a bacterial pathogen.

In some cases, however, phagocytes do not arrive fast enough to the site where the C3b-covered bacterium hangs around. In this case, other complement proteins, such as C5 and C6, begin to spontaneously assemble around C3b and form the so-called membrane attack complex (Figure 6). This complex punctures a hole into the cell surface, which looks like a gunshot wound, causing the bacterium’s innards to spill out and dissolve.

Formation of the membrane attack complex via the self-assembly of complements. Created with BioRender.com.

How does the complement system differentiate between commensal and pathogenic bacteria?

You are probably aware that in your body also live many friendly bacteria, the so-called commensal ones. And you do not want to get rid of these helpful bacteria. Hence, the immune and complement systems have adapted several strategies to keep your friendly bacteria and focus their killing power on harmful intruders.

For example, commensal bacteria reside only in certain areas of your body like the gastrointestinal tract. They do not float around in the blood. Your immune system is aware of this. Hence, the complement system in the gastrointestinal tract is modified and does not attack these commensal bacteria. Instead, their recognition skills focus on harmful intruders.

Also, commensal bacteria contain additional molecules on their surfaces to hide their PAMPs from the complement system. This prevents the complement system from getting activated.

The complement system as the first immune fighters

As you’ve seen, the complement system works tirelessly, day and night, patrolling your bloodstream to ensure that no harmful bacterium gets too comfortable inside. With its sensor proteins, it identifies these pathogens and activates the immune army to clear out any infection.

Hence, the complement system is the crucial first line of defence of our immune system. By recognizing and targeting harmful bacteria and sparing beneficial commensal bacteria, it ensures that your body remains healthy and free from infection.

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Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world

Those bacteria that call your gut their home are the so-called commensal bacteria. Luckily, they have a special superpower: They can protect us from bacteria that cause infections and make us sick. For this, our commensal gut bacteria developed some extraordinary strategies to defend these pathogens.

So, by nurturing our friendly gut bacteria, you are also strengthening your protection against diseases. Here, we will look at what kind of bacterial wars are going on in your gut and how your gut bacteria defend pathogens and keep you healthy.

Your gut bacteria defend pathogens with toxic molecules

Bacteria have many different means to kill other microbes, competitors or even their own siblings. Often, these bacteria produce molecules that are toxic to their prey, which means they inhibit cellular proteins or machineries. Without these machineries, the prey is then lacking an essential cell function to grow or survive, so that it eventually dies.

Interestingly, gut bacteria produce and deliver many different toxic molecules of various shapes and sizes, functions and even origins.

Gut bacteria produce bacteriocins

Many bacteria produce molecules that are like antibiotics specifically to kill bacteria. These are called bacteriocins.

Some bacteriocins are simple and small molecules, while others can be big and fancy. However, they all have a similar goal: they bind to a specific target in the prey bacterium and prevent that target from working properly.

So, no wonder that many bacteria in our gut microbiome produce bacteriocins that are toxic to pathogenic intruders. Also, we carry a lot of different bacteria in our guts and they all produce different bacteriocins. Hence, incoming pathogens face this huge load of toxic molecules making it really difficult to establish themselves in our intestines.

For example, one bacterium that loves the warmth and lack of oxygen in our gut is the bacterium Ruminococcus gnavus. And this one produces at least two bacteriocins, Ruminococcin A and C, that are toxic against human gut pathogens like Clostridium perfringens.

Other friendly gut bacteria, like Escherichia coli or Blautia producta, also produce bacteriocins that are toxic to pathogens, like Enterococcus faecalis. And some of their bacteriocins can even impact our gut cells by activating and strengthening our immune response.

Gut bacteria produce short chain fatty acids from fibres

Another way to protect against pathogenic gut bacteria is directly related to your diet. When we eat a lot of fibres, which are non-digestible carbohydrates, our friendly gut bacteria break these up. From these fibres, they produce small molecules that are called short-chain fatty acids, which have many positive health benefits for our overall wellbeing.

Interestingly, when we have a lot of these short-chain fatty acids in our intestine, the pH drops. This is already pretty difficult for most pathogenic bacteria, as not many can handle this acidic environment.

Plus, short-chain fatty acids diffuse into pathogenic gut bacteria where the pH drops as well. This can disturb many cellular machineries from functioning properly and not many bacteria have the right tools to defend against this attack, so they’ll die.

Gut bacteria convert bile acids into toxic compounds

To better digest the fats in food, our liver produces bile acids. These molecules bind fatty acids and lipids so that we can take them up better into our bodies.

But some of our friendly gut bacteria can convert these primary bile acids from our liver. For example, one of these bacteria, Clostridium scindens, transforms them into secondary bile acids that can bind the lipids of bacterial membranes.

Like this, secondary bile acids open the membranes of some pathogenic gut bacteria, like Staphylococcus aureus, Bacteroides thetaiotaomicron or Clostridoides difficile. This eventually kills the intruders and keeps our guts pathogen-free.

Killing pathogens with bow and arrow

Yes, also direct bacterial wars are happening in our guts! And they are nasty!

Some bacteria use tiny little bows to shoot deadly arrows into other bacteria. And these arrows can be incredibly toxic so the shot bacterium has barely any chance to survive the attack.

Luckily, our gut bacteria use their bows and arrows to defend against gut pathogens. For example, commensal bacterium Bacteroides fragilis has three different bows and can shoot various arrows. And research showed that this bacterial friend can protect us from bacteria that otherwise cause intestinal diseases.

Interestingly, Bacteroides fragilis is not opposed to hit’n’kill its own toxic bacterial siblings since some members of his family can indeed make us sick. But our friendly Bacteroides fragilis collected many different immunity proteins against its evil siblings so that their toxic arrows cannot harm it. Instead, Bacteroides fragilis keeps shooting and killing until we are safe from the pathogenic sibling.

Keeping nutrients from pathogenic gut bacteria

Another important way how gut bacteria defend pathogens is by keeping nutrients away from them. In all mixed microbial communities, bacteria fight for nutrients, especially for metals like iron, zinc but also sulphur sources.

Luckily, our gut bacteria developed some sneaky ways to steal these metals from gut pathogenic bacteria. By sending out special proteins that bind these metals very tightly, the commensals make sure to keep these metals from the pathogens. And if the pathogenic bacteria don’t have enough of these essential metals, they won’t survive and will eventually die.

Strengthening the mucus layer to block pathogenic gut bacteria

When you think about it, your gut is not part of your body – even though it is inside of you. All the food that we eat, stays within this digestion tube (mouth, oesophagus, stomach, intestines) until it comes out on the other side.

And to protect us from harmful microbes and molecules, we need to have a clear physical barrier from the content of the tube. This barrier is the so-called epithelial layer, which is covered by a slimy mucus on the outside. And this sticky slime helps keep off intruding microbes so that they cannot breach through the epithelial wall and get into our bodies.

Luckily, our helpful gut bacteria help us maintain this slimy defence wall. As bacteria produce SCFAs close to the mucus layer, the epithelial wall produces more slime. And if the slime gets thicker, gut pathogenic bacteria have more difficulties getting into our bodies.

To help the slime grow, some bacteria adapted very well to the conditions within the gut. For example, the friendly gut bacteria Akkermansia muciniphila and Ruminococcus gnavus cut off the very end of the mucus layer and feed themselves with them. This does not harm the mucus itself, but it keeps these bacteria close by. And this in turn triggers the epithelial wall to produce more mucus. So, everyone wins.

How to help your gut bacteria defend pathogens

Now, that you better understand how your gut microbiome defends pathogenic gut bacteria, make sure you support them keeping you healthy. By feeding your gut bacteria the right foods, you will help them be comfortable and happy in your gut. And when the right bacteria grow within you, they will gratefully protect you from nasty intruders!

Another idea for researchers is to use what they have learned to keep you healthy. The idea is to develop probiotics or prebiotics that help us defend against nasty pathogens. For example, you might take pills containing toxins against pathogenic gut bacteria or probiotics with bacteria that can fight off pathogens.

Whatever it may be, you can always help your gut bacteria be happy in your intestines by eating the right things. That means lots of fibre and veggies! ?

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Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world

I am fascinated by the impact that these tiny organisms have on our bodies and health, the environment, climate and even food. And I am always amazed by how everything is interconnected; how microbes in the soil can shape the weather and the climate and how microbes in our guts from the food we eat shape both our mental and physical health. Mind-blowing!

With such a huge impact on our lives, microbes even shaped human history, politics, culture and advancement. Due to their integral influence on everything we do, I am convinced that we should all learn more about the fascinating microbes and bacteria all around us.

Sure, this is the main motivation that we write this blog, but there are also great books about microbes that are both educating and entertaining. Here, I want to share my favourite books about microbes and bacteria, written not only to inform but also to make you giggle about what microbes do. I recommend reading any of these microbial books if you’re slightly interested in the microcosmic world or are looking for a present for someone who is.

Disclaimer: some of these links are affiliates and I might make a small profit from your final purchase with no extra costs to you.

I Contain Multitudes: The Microbes Within Us and a Grander View of Life by Ed Yong

This book is already a classic in the microbiology literature. In an easy and funny way, Ed tells the reader how microbes affect our daily lives. After a quick introduction into evolution, Ed talks about how microbes impact our bodies, metabolism or defend us from diseases.

Ed further tells us in a light way that you should not consider your body just as it is, but rather as this multi-organism interacting, communicating and exchanging with the microbes in and on it. After reading this book, you might not see your body the same way as before.

This book about the microbial life is great for:

Everyone who wants to read light stories about microbial life and get a first overview of how microbes have always impacted us and keep impacting everything we do.

Deadly Companions: How Microbes Shaped our History by Dorothy H. Crawford

I started reading this book when the Covid19-pandemic started and felt reassured and scared at the same time. In this book, Dorothy talks about several global pandemics in human history, how these shaped our culture and politics and what we could learn from each one of them.

This book makes it clear that by advancing our communities and cultures, we gave microbes the opportunities to spread amongst us. Like this, infectious disease pandemics have always been part of our history and should be no surprise to anybody.

This book about microbial history is great for:

Everyone who is interested in human history and wants to learn more about how microbes have always impacted human life, especially our politics and culture.

Coloured Bacteria from A to Z from BacterialWorld

We, Noémie and Sarah, wrote and illustrated this book to introduce you to 26 different bacteria, one for each letter. You will get to know bacteria from different environments, their colours, superpowers and how they impact your daily life. In the descriptions for each bacterium, the reader will gain a basic understanding of bacterial cells and growth, microbial fermentation and food production, microbes’ impact on sustainability, antibiotics and health.

With hand-drawn illustrations and a final quiz section, both young children and adults can engage in a relaxing activity while learning about the colourful bacterial world. You can choose among different languages and get the book from Amazon or print the sheets yourself as often as you want.

This microbiology colouring book is great for:

Anyone who has a young child and wants them to learn while colouring. We also found lots of adults who enjoy the meditative activity of colouring and for whom this microbiology colouring book might be a thoughtful present.

Joyful Microbiology Activities Ebook by Justine Dees

Even though microbes are all around us, it is often difficult for students to grasp their omnipresence. The Joyful Microbiology Activities book brings microbiology to your home and shows you with well-explained and hands-on experiments where you can find microbes and bacteria.

A bucket list of the different locations to check out and look for microbes as well as a colourful photo atlas with images of lichens, molds and fungi helps students and curious kids get interested in the world of microbes. Justine also prepared follow-up questions and more ideas for projects and exercises, so parents and teachers can take their microbiology activities one step further.

This book about microbiology activities is great for:

Teachers with science classes as these activities are suitable for class experiments and students of multiple ages. Parents who want to awaken microbiology curiosity in their kids.

The Mind-Gut Connection: How the Hidden Conversation Within Our Bodies Impacts Our Mood, Our Choices, and Our Overall Health by Emeran Mayer

Emeran wrote this book for people who are interested in the little details of how microbes impact our bodies. He talks about the molecular communication between gut microbes and the rest of our body and tells the reader what they can do to positively influence this interaction.

From this book, you will also learn what that gut feeling actually is and why sometimes things just feel right or why you have butterflies in your belly when you’re excited or meet a new love. Emeran also explains why a plant-based diet is the right food for your gut microbes and which food additives you should avoid to stay strong, happy and healthy.

This book about gut bacteria is great for:

Everyone who wants to dig deeper into how microbes impact our health, mood and behaviour and wants to learn in detail about how the human body and brain work.

Invisible Friends: How Microbes Shape our Lives and the World around us by Jake Robinson

This book surprised me a little about its content. Expecting another book introducing the world of microbes, this book instead talks from a social science perspective about how microbes touch our lives. I still haven’t understood the storyline and the key message of the book, but hope it will reveal itself as I get to finishing the book.

Books about microbes and what to learn from them

Here you have six books about how microbes shape your health, the environment and even human history. These are written in languages as jargon-free as possible. And when the authors use technical words, they explain exactly what they mean.

Like this, your background doesn’t matter. As long as you’re interested in the microbial world, you will easily follow these books.

Do you have a favourite book about bacteria or microbes? Make sure to share them in the comments below, so that others can learn more about the fascinating microbial world as well!

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Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world

You touch your face when it itches. You touch surfaces in a house. Even when you lay down in bed, you touch your phone or the bed itself.

Remember that this is a microbial world, and microbes are everywhere: on us, in us, and around us. People and their skins interact with microbes. And microbes interact with us via our skin.

About the bacteria on your skin

The skin is the largest human organ. It acts as a barrier against intruding bacteria and pathogens.

With more discoveries in the field of the human microbiome, scientists figured out that our skin also has its own microbiome. The hand microbiome is particularly interesting for public health research since we often transmit diseases via our hands.

Plus, your index finger is your most used finger. Hence, it has the greatest variety of microorganisms.

So, if you think about it; hands are never REALLY clean and people touch A LOT of things all the time.

The day to day life of your hand microbiome

During the day, we and our hands interact with a lot of different environments. All these interactions impact our hand microbiome. This means that hands do not harbor a constant, unchanging microbial community; on the contrary, it changes pretty rapidly.

Therefore, scientists cannot specify or define what is a “healthy hand microbiome”. But, what we know is that the hand microbiome of every individual can have “good” (beneficial) and “bad” (pathogens) bacteria.

“Good” or “beneficial” bacteria are the ones that live in symbiosis with humans. This symbiotic relationship is known as mutualism. This means that both humans and bacteria benefit from interacting with each other. Bacteria protect against pathogens and support the host’s immune system. Humans provide the environment – the skin – and nutrients to help microorganisms grow.

“Bad” or “pathogenic” bacteria, on the other hand, come from the environment. They can cause diseases like acne because they know how to trick our immune system. That’s why we are taught to wash our hands to get rid of these types of bacteria and avoid getting sick.

When scientists looked at what the average hand microbiome could look like, they found that bacteria are the most common microorganism. Additionally, viruses and fungi are less common in the skin microbiome of our hands. They make up less than 5% of the found microorganisms.

Factors influencing the skin microbiome of our hands

As we saw above, many factors influence what our hand microbiome looks like. And it turns out that your lifestyle has the greatest impact on your hand microbiome.

Just think about your diet, where and how you do exercises, or even about your job… All these factors impact which microbes settle down on your hands and become part of your skin microbiome.

And would you have thought that gender also influences the microbial community on your skin? Yes, it is proven that, overall, men and women have different bacterial profiles on their skin. No one knows why such a difference exists. It could be one of those things that distinguish men and women on a biological level.

Also, let’s not forget about external circumstances affecting your hand microbiome. Every time you step outside of your house, your skin microbiome changes.

Scientists also found that members living in the same household have similar hand microbiomes. So, even though every individual has their own unique collection of microorganisms on their hands, living in the same space makes them more similar to one another.

Additionally, if you own a dog, your hand microbiome and microbial community on your pet’s paws become more similar to one another. By interacting with your pet throughout the day, the microbes on your hands can exchange with those on your pet. Who knew that pet ownership can increase the diversity of bacteria on your hands?

Many different microorganisms live on our personal belongings, like cell phones and keyboards. These microbes likely come from our skin microbiome because those objects are, by far, the most touched throughout the day. Some scientists even think of introducing microbiome analyses of personal objects as an alternative to human DNA forensic investigations.

How can studying the skin microbiome help us?

Hands are like busy intersections, connecting our microbiome with the microbiomes of other people, places and things. Even a slight interaction with an inanimate object in your house can change what your hand microbiome looks like.

So, what can we learn from studying the hand microbiome? Our hand microbiome is like a second fingerprint. Hence, experiments in this field can uncover information on how to use a hand microbiome as a diagnostic tool.

Such a microbial tool would speed up the diagnosis process! By building general microbial profiles of every patient, doctors would be able to target only those areas that need immediate attention. And this would mean fewer prescriptions of broad-spectrum medications!

The post Bacteria on your hands strengthen your unique skin microbiome appeared first on Bacterialworld.
Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world

However, some bacteria found a way to become invisible in front of the immune cell army. They put on an invisibility cloak so that they can sneak into the human body without being seen. This invisibility cloak is a so-called bacterial capsule. And pathogenic bacteria use capsules to trick the immune system to infect our bodies.

Here, we will explore what bacterial capsules are and how bacteria use them to overcome our immune systems.

About bacteria with capsules

Bacteria that produce capsules are generally pathogens. These are bacteria that can infect us, cause disease and make us sick. And bacterial pathogens use capsules for the infection process. Without capsules, pathogenic bacteria would be eaten and killed by our immune cells.

Bacteria with capsules are for example Klebsiella pneumoniae, Mycobacterium tuberculosis, Haemophilus influenzae, pathogenic and uro-pathogenic Escherichia coli, Neisseria meningitidis and Porphyromonas gingivalis.

Many people carry Klebsiella pneumoniae in their gastrointestinal tract or nose without having any symptoms. However, in some people, this bacterium can enter the blood circulation and cause infections like pneumonia, sepsis, urinary tract infections, bacteremia or meningitis.

The pathogen Mycobacterium tuberculosis causes the devastating disease tuberculosis with almost 1.4 million deaths every year. Haemophilus influenzae infections lead to sinusitis and uro-pathogenic Escherichia coli causes urinary tract infection. Another awful pathogen is Neisseria meningitidis. This bacterium infects the membrane around our brain and leads to the disease meningitis. Lastly, Porphyromonas gingivalis is an oral pathogen that infects and destroys the tissue around our teeth. You might know this disease as periodontitis.

This list of pathogenic bacteria might sound a bit frightening. But it is to highlight the one feature they all have in common: These bacteria use their capsules to enter our bodies and cause these diseases.

So, let’s have a look at what this capsule actually is.

What are bacterial capsules

The bacterial capsule is a thick layer of a sugar-water mix that surrounds the bacterial cell.

The capsule layer consists of long chains of sugar molecules that are attached to the bacterial cell surface. These sugar molecules have different lengths, lots of branches and different attachments. The sugar chains absorb water molecules so that a gooey slime develops. Researchers can even see this under the microscope.

Interestingly, different bacteria can produce chemically identical capsules. But the same bacteria can also produce different capsules. In this case, bacteria add little attachments to the outer tip of their sugar branches. Now, this bacterium “looks” completely different from the outside.

Generally, antibodies bind to these sugars, which is why we call these sugars antigens. However, when bacteria change their sugar tips, they also change their antigens. Hence, another antibody is needed to recognise this new antigen – even though it might still be the same sugar. In this case, we call the bacterium with the new sugar antigen a serotype.

For example, researchers found 80 different antigens and thus serotypes in Escherichia coli based on their capsule sugars. And for Streptococcus pneumoniae, they even identified 93 serotypes.

Now, you might ask yourself what is the function of capsules in bacteria?

Bacterial capsules are invisibility cloaks

A bacterial capsule works like an invisibility cloak. As soon as a bacterium enters the dark halls of our human bodies, it puts on the cloak. Now it won’t be seen by the immune guardians. Like this, bacterial pathogens follow the model of “the best defence for a pathogen is a good defence”.

The players of our immune system recognise and bind to specific molecules on the surface of bacteria. This activates the immune system and attracts more phagocytes. These immune cells eat intruding pathogens and destroy them. Like this, our immune army is always ready to fight the bad guys.

However, the bacterial capsule hides these surface molecules that our immune system usually recognises. Like this, our immune players cannot bind these sugar-coated pathogens. This keeps the immune army deactivated. Now, bacteria can escape the immune system, sneak into our bodies and cause infections.

Our immune system can also fight intruding bacteria by producing antimicrobials. Yet, the sugar capsule of some bacteria can absorb these small molecules and make them useless. Hence, the bacterial capsule acts as a protective layer against immune attacks.

Neisseria meningitidis even has a “capsule-switch”. Once activated, it can cover itself with another sugar layer that looks completely different from the outside. The immune players need to learn again to recognise this new layer, which takes time. Hence, with this “hyper-encapsulation”, Neisseria meningitidis can escape the immune system again.

Overcoming bacterial capsules

Because bacterial capsules are at the outer surface of a bacterium, researchers want to use these components as targets for vaccines. However, since bacteria can change their capsular components, these targets are not very reliable. So, researchers are working on developing vaccines that recognise different serotypes.

For example, a vaccine that recognised different antigens of the capsule in Klebsiella pneumoniae was developed and reached clinical trials. However, the high costs of such an efficient vaccine made this project difficult.

Another approach is to better understand how pathogenic bacteria regulate their “capsule-switch”. If we can prevent bacteria from putting on another cloak, we can help our immune system do its job and kill intruding bacteria. Hence, researchers are looking for ways to achieve this.

Bacterial invisibility cloaks – another way for bacteria to survive

You might now think how nasty bacteria are for using such a capsule to escape our immune system and infect us. However, for bacteria, this is another survival mechanism. If they do not put on their invisibility cloak, the immune system will eat and kill them. So, some bacteria developed this mechanism to overcome their foes.

And I think it is a pretty smart way to survive.

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Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world

But have you ever asked yourself where yogurt comes from and how it is made from milk? Do you know why yogurt tastes so sour and yet delicious?

What if I told you that yogurt only tastes like this thanks to bacteria and their superpowers?

Yes, bacteria not only produce delicious chocolate, wine, beer or bread. But it is also bacteria that make yogurt from milk.

Here, we will look at which bacteria produce yogurt and what makes it so creamy, sour but also healthy.

What’s in your yogurt?

Yogurt would not exist if it wasn’t for our bacterial friends. Interestingly, it only takes two bacterial species to create this white creamy dream that we call yogurt. These two bacteria are Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus.

Within milk, these two bacteria live in a symbiotic relationship. This means they help each other grow and survive. And together, they produce delicious yogurt.

These two bacteria make many molecules that give yogurt its characteristic flavor. These include lactic acid and other acids like acetoin, acetate, acetaldehyde. Because of all these acids, yogurt tastes quite sour.

Also, our two bacteria produce exopolysaccharides. Generally, bacteria use these to make biofilms. But in this case, the exopolysaccharides with their long sugar chains make the yogurt creamy and viscous.

Thanks to bacteria and the milk content, there are also a lot of healthy molecules in yogurt: proteins that are rich in energy, calcium, and vitamins B2, B6 and B12.

How is yogurt made?

It seems that all we need to make delicious yogurt are milk, our two bacterial species Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus and the right temperature. We call these two bacterial species the yogurt starter cultures.

But before their superpowers produce yogurt from milk, the milk needs to be prepared. This is basically to get rid of all the other stuff that we don’t need.

So, to kill all other microbes that might spoil our yogurt, the milk is heated to 95 °C. You might know this process as pasteurization.

After the milk cooled down to about 40 °C, our two starter bacteria are added. Next, the mix is filled into cups and sealed. The cups are then stored in a warm room – something researchers call incubation. During this incubation time, the bacteria can get to work and use their superpowers.

This means that our two bacteria start a process called microbial fermentation. They break down the milk sugar lactose and produce lactic acid and other acids.

Due to all the acids, the pH of the milk drops and it becomes sour. Now, the acids denature the milk proteins – this is the same process that you see when you heat an egg: it becomes harder and loses its fluidity. The milk becomes more viscous and gets a gel-like texture and creaminess.

Why is yogurt good for you?

We already saw that yogurt has a lot of good stuff and some studies showed that it is healthy for us because of all these molecules. But how do these vitamins, proteins and short-chain fatty acids impact our health?

For example, yogurt stimulates the immune cells that are in our guts. This improves our immune system so that it can better fight bad intruders.

Our two starter bacteria also break down some of the milk proteins and produce so-called bioactive peptides. Our guts like these peptides a lot. Hence, it transports them into our bodies where they have health benefits.

Also, the sugars in yogurt are prebiotics. This means they are the right food for other bacteria that live in our guts and that keep us healthy.

Plus, yogurt is full of protein that our bodies need to grow muscles and stay strong. Interestingly, yogurt protein has two important fractions: whey and casein protein.

The whey protein is considered a “fast protein”. This means, our body digests this type of protein faster which gives us energy immediately after eating yogurt.

The other fraction is casein or the “slow protein”. This type of protein clots in our stomach because of the acids. But our body can digest this protein clot only slowly. Hence, the casein protein gives us energy even up to 7h after eating yogurt. Like this, yogurt helps with satiety so that in general we need to eat less.

Lastly, the short-chain fatty acids in yogurt have lots of health benefits for us. They regulate the blood glucose level, insulin resistance and inhibit our appetite.

Now you have a lot of reasons to include yogurt in your daily diet plan!

What is probiotic yogurt?

Researchers found that the two starter bacteria Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus do not survive the acidity in our stomachs. Hence, they do not arrive in our guts and have no impact on our gut microbiota.

However, yogurt is a great vehicle to transport other probiotic microorganisms into our bodies. Probiotics are organisms that “when administered in adequate amounts, confer a health benefit on the host”. Also, probiotics need to be safe, well-characterized and stable while the yogurt is waiting on the shelf to be eaten.

Hence, many yogurt companies now add beneficial probiotics to yogurt. These are bacteria like Lactobacillus casei, Lactobacillus acidophilus or Bifidobacterium.

These bacteria have beneficial effects on our digestion and immune system. They help the right bacteria in our guts to grow, meaning they keep our gut microbiota healthy.

For example, in one study, researchers added a Lactobacillus casei species to yogurt and gave it to children with acute diarrhea. After a few days, these children had fewer symptoms and less abdominal pain thanks to the yogurt mix.

Is (probiotic) yogurt on your diet plan yet?

Here, we looked at two new superhero bacteria that produce the fermented creamy white dream. Even though they might not survive the passage into our bodies, they produce a lot of healthy molecules for us. Hence, they have an indirect health benefit on our bodies.

Plus, yogurt is a great vehicle to transport other probiotic bacteria into our bodies. And it seems that by eating yogurt regularly you can indeed change your gut microbiome and bring in some helpful bacteria.

So, thank bacteria for their superpowers and for providing us with this delicious food!

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Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world

Many of our organs have a slimy mucus which is supposed to stop bacteria from entering the human body. But some bacteria developed mechanisms to swim through this gel-like mucus faster than others.

And these bacteria are usually the ones that make us super sick.

Meet the bacterial race swimmer Campylobacter jejuni

The pathogenic bacterium Campylobacter jejuni for example causes food-poisoning and watery diarrhoea. And this pathogen can swim through gel-like slimes, like the mucus in our bodies. Other bacteria are slowed down by this slime, but not Campylobacter jejuni. It even swims faster when it hits slime!

Why is that?

Well, that is exactly what researchers were trying to find out.

Two flagella for one movement

Campylobacter jejuni looks pretty cool. It has a helical shape and one flagellum on each side of the cell. Flagella are like fine hair that grow out of the bacterium. 

Closer to the membrane of the bacterium, the flagellum becomes a so-called hook. This hook is connected to a little motor inside the bacterium. And this motor rotates, which then rotates the hook and thus the flagellum. Now, the flagellum works as helical propeller and this movement pushes the bacterium forward so that it swims.

Since Campylobacteria jejuni has two flagella of different length, researchers were curious about how this bacterium would move. Two motors would constantly push the bacterium in the opposite direction. Plus, they saw previously that this bacterium can swim faster than other bacteria in slime. But they had no idea how these two flagella would work together. 

Wrapped in flagella

To see the flagella under the microscope, they changed them slightly. Like this, they could stain the flagella and see them as yellow fluorescent tails under the microscope.

They saw that in watery liquids, half of the bacteria had both their flagella spread to both sides and they were swimming slowly. This you can see on the left side in this video. The other half had one flagellum rotating as a tail at the back and the other flagellum was wrapped around the bacterial cell.

In gels (in the video on the right) almost all the bacteria (>95%) had one of their flagella wrapped around their cells. Plus, these cells swam faster and more directed. Mind-blowing!

Two motors are better than one

So, the researchers wanted to know why Campylobacter jejuni wraps the flagellum at the front around its cell and how that helps the bacterium to swim faster. They created two mutants of this bacterium: One bacterium did not have a front-flagellum and the other did not have a tail-flagellum. 

And they looked at how these mutants swam in comparison to the bacterium that has two flagella. In the video below, you can see the bacterium with two flagella on the left, the bacterium with the tail-flagellum in the middle and the bacterium with the front-flagellum on the right.

And as you can see, the bacteria in the middle had their tail-flagellum propelling. This pushes the bacterium forward so that it swims. Bacteria with the front-flagellum still swam. And the researchers confirmed that this front-flagellum is still rotating. It works as if it drills the bacterium forward.

So, when bacteria have two flagella, it has double the power; and the pushing and drilling together makes this bacterium super fast.

Changing direction

Next, the group was interested to see how Campylobacter jejuni changes its swimming direction. Luckily, they managed to film one bacteria at the moment when it decided to swim towards the other side.

In this video, you can see that first the front-flagellum changes the direction of its rotation. Like this, it is getting unwrapped from the bacterium.

Then, the tail-flagellum also changes its direction of rotation and the bacterium halts its movement. This looks as if the bacterium tumbles trying to get to the new direction.

Next, the former tail-flagellum wraps around the bacterium and becomes the front-flagellum.

And the former front-flagellum becomes the tail-flagellum and rotates to push the bacterium towards the opposite direction.

Two flagella to get to the perfect location

Researchers already knew that other bacteria also wrap their flagella around their cells. But often this happens in trapped places so that the bacterium tries to protect its flagellum. However, Campylobacter jejuni with its two flagella developed some efficient mechanisms to infect the human body. 

• Its helical shape helps the bacterium to drill through slimy mucus

• A rotating front-flagellum pulls the bacterium actively forward helping with the drilling movement of the bacterium

• The tail-flagellum rotates to propel the bacterium forward

• By quickly changing its swimming direction, Campylobacter jejuni can escape from confined spaces or maybe even immune cells in the human body

I’m always amazed by what bacteria come up with to escape dangerous situations…

So, now that we better understand how this pathogen moves in our bodies, we better understand how it infects us. This knowledge will now help to fight this pathogen. Let’s hope that it will help us get rid of such nasty food-poisoning-causing bacteria. 

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Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world

Vaccines helped eradicate deadly diseases like smallpox.

And for over a century, researchers developed vaccines according to Pasteur’s principle. They isolated the microorganism and inactivated it. Then they injected the now harmless microorganism into people. 

Now these people were vaccinated.

Their immune systems would detect this foreign microorganism and develop antibodies against it. The next time this person gets infected with the real microorganism, the antibodies would be ready to fight the intruder.

New challenges for researchers

But unfortunately, developing vaccines is not always that easy.

Especially, when researchers have trouble growing an organism in the lab. As it is the case with the hepatitis C virus. And then there are nasty pathogens like Neisseria meningitidis. These know too well how to hide from the immune system and cause deadly meningitis. Or to fight a clever virus like HIV, we need help from extra skilled parts of our immune system. Let alone a virus as SARS-CoV-2 that emerged from nowhere and for which we need a vaccine real quick.

To develop vaccines against these microorganisms, researchers needed a new strategy. They try to find new vaccines that activate the immune system and trigger it to produce antibodies. These antibodies have to detect a specific piece of foreign microorganism. Often, this is a protein from the surface of the virus or the bacterium: the so-called antigen. 

But not every antigen is a good antigen that activates the immune system.

Hence, researchers need to produce and test different antigens. And for this, they rely on fancy technologies and super-efficient helpers: bacteria. Here, we will look at how researchers use bacteria in the hunt for vaccines. 

Bacterial pets in the lab

For some researchers, the bacterium Escherichia coli is a dear lab pet. They know exactly how to grow, change, regulate, mutate, shock and kill this bacterium. And they appreciate that their favourite lab bacterium can carry big chunks of DNA and produce almost any protein.

So, to produce and test antigens, researchers need to make DNA with a gene for an antigen.

Bacterial machines to produce DNA

To produce any piece of DNA, researchers use a special DNA production machine from the bacterium Thermus aquaticus. This bacterium lives in hot regions, so its enzymes only work at hot temperatures. 

Hence, researchers can control this DNA production machine by regulating the temperature. And like this, they can produce any gene they need.

Bacterial machines to cut and paste DNA

The problem is that the gene alone is not stable. This is why researchers need to put this gene (in blue in the picture below) into a plasmid. Plasmids are stable DNA circles (in yellow), that bacteria recognise and produce. 

To link these two pieces of DNA together, researchers use special scissors. These scissors cut the gene and the plasmid so that they now work like puzzle pieces. They can only fit together. 

These scissors also come from bacteria and, interestingly, every bacterium has its own type of scissors. This means researchers can produce many different puzzle pieces that always work in pairs.

Next, the plasmid and the gene need to be glued together. And for this, researchers use a glue stick from a virus. And yes, it works like the plaster in the picture.

Finally, we have a big chunk of DNA with a gene for an antigen.

Now, researchers need to produce this antigen.

Guess what, they use bacteria for that too!

Bacteria are protein production machines

First, the plasmid with the gene for the antigen needs to go inside the bacterial cell. For that, researchers electrocute the bacteria together with the plasmid. Yes, electrocute them! Poor bacteria!

But this brings the plasmids into the bacteria.

Next, researchers grow these bacteria with the plasmid. The bacteria now produce a lot of that plasmid and a lot of that antigen (blue).

Next, researchers need to kill the bacteria and clean the antigens from them.

With all the antigens produced now, the fun experiments can get started. 

Finding the best antigen for a vaccine

Generally, researchers produce many different antigens to find the best one as a vaccine. The best antigen is the one that binds to an antibody the tightest.

To test all the antigens, researchers do an experiment that is funnily called ELISA. And they can do this ELISA experiment only thanks to bacteria.

Some bacteria from the Streptomyces family produce the protein streptavidin. This protein binds very, very tightly to the vitamin biotin. Obviously, researchers make use of these two proteins in the lab.

In the simplest version of an ELISA experiment, researchers glue antigens to a surface (yellow, blue and green). Then, they add liquids with different antibodies (grey) to these antigens to test which one binds most tightly. 

These antibodies are linked to a biotin molecule (grey circle). Next, the researchers add streptavidin (green) that is linked to an enzyme. Now, only if the antibody bound the antigen, the streptavidin can bind the biotin. And if that happens, the enzyme can change the colour of the liquid. 

Like this, researchers can test many different antigens and “see” for which the colour changes. These are the ones that bound to an antibody.

Researchers need to repeat all these steps many times; each time changing the antigen a bit to make it more efficient.

But eventually, this antigen becomes a vaccine.

And just as bacteria produced the antigen in the lab, they might have to do that in large amounts to produce the masses of vaccines needed.

About vaccines produced by bacteria

Bacteria can produce different proteins and therefore different vaccines.

For example, the vaccine against the hepatitis E virus is completely made by bacteria. Bacteria produce the envelope proteins of the virus. These then assemble and build the virus structure. This vaccine now has the same structure as the virus, but it is inactive and harmless since no viral DNA is inside the envelope. 

Some vaccines also have components from different organisms. 

Our immune system can very well detect the sugars on the surface of bacteria. Hence, researchers attach some of these sugars to vaccines. Like this, they attract the big players of the immune system to the vaccine. This activates the immune system so that it develops antibodies against the vaccine.

Researchers also linked bacterial proteins to vaccines. Here, researchers found that bacterial toxins or proteins from the bacterial surface attract and activate the immune system. But not to worry, researchers worked out how to inactivate the toxin so that the vaccine is not harmful.

Not all vaccines are produced by bacteria

Lastly, researchers developed new strategies to produce vaccines without bacteria. And they even use this strategy for some vaccine candidates against SARS-CoV-2 that causes the COVID-19 disease.

These vaccines only contain a piece of RNA enveloped in a lipid membrane. And, yes, this concept looks a lot like bacterial outer membrane vesicles that transport DNA or drugs. 

In this case, our body produces the protein – the antigen – from the RNA. This again activates the immune system and triggers it to make antibodies against the antigen.

So while the delivery mode of the vaccine is pretty different, the way to activate the immune system is still the same.

Bacteria are important in the hunt for vaccines

Some microorganisms are real burdens to the world population. Hence, researchers had to come up with new strategies to tackle them. There is no vaccine against the nasty SARS-CoV-2 yet, and maybe the final vaccine will be produced completely independent of bacteria. But still, bacteria are massively helping researchers in the lab. 

They are amazing little machines to produce proteins or transport DNA or drugs. And they evolved helpful enzymes that every lab researcher uses daily. No biology-related research would work without the amazing mechanisms of bacteria.

Ever since the pandemic started, a lot of people ask me whether we can have bacteria kill the nasty SARS-CoV-2. I doubt it will be a direct fight between bacteria and viruses. But I am convinced that in the end bacteria and their superpowers will save this planet.

Researching and writing this post was possible due to the Journalism Research Grant from the Berlin Science Week.

it’s been a great first adventure as a proper science journalist at the #BerlinScienceWeek https://t.co/ZlJFOb9e18

— Sarah Wettstadt (@DrBommel) November 6, 2020

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Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world

Bacteria become resistant to antibiotics. 

Cancer spreads like never before. 

And a virus determines how we live our lives. 

Why do we need to transport drugs within our bodies?

These three major problems need researchers to develop new drugs, like new antibiotics, efficient chemotherapeutics, or long-lasting vaccines.

But we also need to transport these drugs into our bodies and to a specific location. This could be the site of a bacterial infection or the tumor that we’re trying to kill. 

For this, researchers have been working on new delivery methods to transport drugs to a specific site. And, interestingly, many of these methods are based on bacterial mechanisms. So, we felt it was more than worth discussing some of these mechanisms here with you. This will show you another way of how bacteria can save this planet by transporting drugs within our bodies.

Let’s dig in.

Outer membrane vesicles

In Bacteria firing toxic bubbles, we learned that Gram-negative bacteria can form bubbles of their outer membranes. These bubbles are called outer membrane vesicles and they can be filled with stuff.

And researchers also tried to use these bubbles to deliver drugs.

Luckily, our immune system can recognise and respond to outer membrane vesicles. This means our bodies can produce antibodies against the surface of these outer membrane vesicles. 

Outer membrane vesicles carrying stuff on their surface

For example, researchers made the bacterium Escherichia coli produce outer membrane vesicles. Only the lipids of the vesicles – nothing else. They then gave these outer membrane vesicles to mice. These outer membrane vesicles were not dangerous and the mice did not produce antibodies against them.

Then the researchers engineered the vesicles. Between the lipids, the vesicles now carried proteins from the pathogenic bacterium Acinetobacter baumanni. Hence, the protein becomes a so-called antigen. This means, that the mice produced antibodies against the antigen. This made them immune against an Acinetobacter baumanni infection. 

This is an option of how to transport antigens into our body to make us immune against different pathogens.

Outer membrane vesicle bubbles filled with stuff

Another way of using bubbles from bacteria to transport drugs is by filling them with stuff. 

For this, the outer membrane vesicle carries a specific protein. This protein fits like a key to a lock of a certain cell type. Like this, the outer membrane vesicle can dock onto a specific human cell and interact with it. 

Just as you can see in the picture above how outer membrane vesicles are formed, this mechanism can also work the other way around. An outer membrane vesicle can “melt” into a human cell. Then, the content of the outer membrane vesicle flows into the human cell. 

For example, researchers engineered outer membrane vesicles and filled them with a chemotherapeutic. This outer membrane vesicle then specifically melted with cancer cells and shed their content into these. This did not completely kill the tumour but inhibited its growth.

Researchers also developed new vaccines that have DNA or RNA inside these lipid membranes. Read more about vaccines made by bacteria.

As exciting as this mechanism sounds at the moment, it still requires more research to fully understand how we could use outer membrane vesicles as drug-delivering vehicles.

Magnetosomes – bubbles following a magnetic force

Magnetosomes are similar to outer membrane vesicles, as they are bubbles made of a lipid membrane. But in How bacteria read and follow the Earth’s magnetic field, we learned that magnetosomes also have iron-clusters that make them magnetic.

Researchers have the idea to guide magnetosomes with a magnet to a specific location in our bodies. Like this, magnetosomes can go deep into tumour tissue and work their magic there.

Now, similarly to outer membrane vesicles, magnetosomes can be filled with drugs like antibiotics or chemotherapeutics. These drugs are then shed into tumour cells or into the surrounding of tumour cells. 

So far, researchers showed this method in mice. They filled magnetosomes with a vaccine against a tumour, gave them to the mice and held a magnet right next to the tumour. This treatment protected the mice from the tumour and could be used at some point in the clinic. 

Bacterial ghosts – a shell of a dead bacterium

Ghosts of bacteria in your body? That is certainly a science fiction idea.

For this, researchers grow bacteria in the lab and engineer them to produce a protein of interest. This could be for example an antigen that will trigger an immune response in the human body. 

When the bacteria are fully grown, researchers trigger them to produce massive tunnels in their outer membrane. All the content of the bacterial cell will flow out into the surrounding. This means, the bacterium itself is dead and cannot grow anymore. But the bacterial envelope with the antigen is still stable. 

Studies showed that bacterial ghosts with antigens triggered antibody production in rabbits.

In another study, researchers filled the bacterial ghosts with anti-cancer drugs. Fortunately, the bacterial ghosts release the drugs very slowly. Like this, the drug is administered over a long time and is thus more efficient. However, researchers did these basic experiments only on cell lines so far. Hence, a lot more research is required to better understand this mechanism of drug delivery.

Living bacteria to transport drugs

Transporting drugs in the body using living bacteria sounds pretty challenging. But researchers know how to engineer strains that have no damaging effects on our bodies and our immune system. 

Using living bacteria to transport drugs in the body even has many advantages.

Bacteria are attracted by certain chemicals

Bacteria do chemotaxis which means they are attracted by certain chemicals or molecules. 

For example, some bacteria are attracted by areas with low or no oxygen at all. Cancer tissue generally lacks oxygen and the surrounding tissue has very low oxygen concentrations.

Hence, some bacteria are already directly attracted by tumours or cancer tissue.

Also, researchers are trying to engineer bacteria that are attracted to other chemicals. For example, they improve chemotaxis in some bacterial strains. And now these bacteria are more efficient in recognising certain molecules within tumour tissue.

Bacteria move with their flagella

After being attracted by a certain molecule, bacteria actively swim towards this molecule. For this, they use their flagella and pili. 

Hence, this swimming behaviour brings them efficiently to the site of infection.

Bacteria produce drugs on the spot

Bacteria are drug production machines. 

Generally, researchers engineer bacteria in a way that they start producing drugs only when they reach a specific location.

Like this, bacteria produce the right drug at the right time and the right location. 

And they can even produce multiple different drugs. How efficient!

Bacterial hybrid delivery systems – Microbots as the future?

Using a hybrid system between an engineered bacterium and a non-living unit sounds a lot like science fiction. These systems are even called microbots or bactobots. But also here, they have only been tested in the lab, and no studies on humans were done yet (at least to my knowledge!).

A microbot consists of a bacterium that does chemotaxis. So, they could be attracted to tumours or cancer tissue.

And this bacterium carries a nanoparticle that is filled with a drug. Like this, the bacterium steers the particle, and thus the drug, to the place of infection. Here, it can release the nanoparticle, which can now work its magic.

So far, researchers showed in a preliminary study in mice, that bacteria can successfully deliver nanoparticles covered with DNA into specific organs.

However, there are still so many obstacles to consider. But it certainly sounds like a promising and very efficient science-fiction idea.

Bacteria and their organelles can transport drugs within our bodies

Here, I showed you some ideas of how researchers are trying to use bacteria or their organelles to transport drugs within our bodies.

We looked at “bacterial organs” like outer membrane vesicles or magnetosomes. These could carry drugs and deliver them to certain body tissue.

We then discussed how researchers are trying to better understand bacterial ghosts to use them as drug vehicles.

And we explored living bacteria and why researchers think they can use them to transport drugs within our bodies.

Microbots, however, sound like science fiction so far. But, who knows, maybe at some point, we will eat a bacterium that carries a nanoparticle filled with drugs.

I hope we could yet again show you a fantastic way of how bacteria can save our medical problems and thus our planet. So, now is the time to lose the fear of bacteria and believe in them. 

Together with bacteria, we can save this planet.

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Bacterialworld - A blog about bacteria: from scientific studies to vivid stories about the fascinating bacterial world