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10 Types Of Bacteria That Live Inside Humans

Last Updated: 29.11.21


You may find it difficult to imagine, but the human body is home to many bacteria, fungi, and viruses, and not all are malign, and you can see this article for more information on the topic. They are invisible to the naked eye, but a digital microscope for iPhone may be enough to help you see them in all their glory. Here are some microorganisms that live inside your body without your knowledge.

Staphylococcus epidermidis

By its name, you might be able to tell that these bacteria like living on the skin. While your entire skin is game for what they do to thrive, there are certain areas that the bacteria prefer. For instance, they are the reason why our armpits smell. That’s the kind of place they like, and the armpits are just part of it.

While you may not enjoy the fact that the Staphylococcus epidermidis bacteria practically make you smell bad, they have an essential role, which is to keep malign bacteria, like the Staphylococcus aureus, at bay.


Streptococcus salivarius

This is a type of bacteria that live inside the mouth. Also, it lives in the digestive tract, and it is one of the first microorganisms we are exposed to right after birth. While it regulates inflammatory processes in the body and it is mostly harmless, the Streptococcus salivarius can be considered what experts call an opportunistic pathogen.

However, the good outweighs the bad in this case and the fact that these bacteria can attack and even kill harmful bacteria like listeria and Staphylococcus aureus make them our allies.


Lactobacillus acidophilus

Most of the bacteria found in the human body reside in the intestines, and the Lactobacillus acidophilus is one of them. It has quite an important role, as it breaks down lactose and produces what is called lactic acid. It is a probiotic and plays a vital role in the health of your gut.

Escherichia coli

coli, as it is known for short, has a bad reputation, as contaminations and illnesses have been reported in relation to these bacteria. There is a particular strain that is rightfully blamed for the pathogenic effects it has on human health, but there are plenty of other strains that are not malign.

Actually, besides being harmless, these bacteria help the overall health of the digestive tract. They live naturally inside the human body, and also in those of some animals.


Methano-brevibacter smithii

Other bacteria that live happily inside the gut carry this difficult to spell name. Their primary role is to break down complex sugars, and therefore they are essential for the proper functioning of your digestive system.

As bacterial fermentation takes place inside the human gut, a large quantity of hydrogen is released. When this becomes too much, the processes taking place here are slowed down, and there is less yield of energy from breaking down foods like the ones mentioned. That is where the Methano-brevibacter smithii intervenes by reducing the amount of hydrogen.


Bifidobacterium longum

Another type of gut bacteria that keep us healthy is the Bifidobacterium longum. It is a probiotic, and its primary purpose is to bind with the cells that make the walls of the intestines. This way, the bacteria create a system of defense that doesn’t allow harmful bacteria to go through.

These bacteria are resistant to gastric acid and bile, and that’s how they manage to live in a highly acidic environment that is your stomach. Like many other probiotics, they play an essential role in keeping not only your gut but your entire body healthy.

Bifidobacterium bifidum

While yogurt commercials might overuse the name of these bacteria, you should know that their role is paramount in your digestion. They also are the guardians of our immune system, and they maintain the proper balance between benign and malign bacteria inside the body.

These bacteria are the most common, and it is safe to say that human life would not be possible without them. Any imbalance in their presence might open the gate to pathogens and illnesses, which is why it is essential to maintain a healthy flora inside our gut.


Enterococcus faecalis

Living in the gastrointestinal tract, the Enterococcus faecalis is, most of the time, harmless, and it plays a role in keeping you healthy. However, for people with a weakened immune system, these bacteria can create the perfect environment for disease.

If there’s a wound and these bacteria get into the bloodstream, they can cause severe infections. There is also a problem with the fact that they can be resilient to antibiotic medicine and they can survive in any environment. That makes treating infections with the Enterococcus faecalis quite tricky.


Toxoplasma gondii

If we have talked so far about bacteria living on the skin and inside the body with a role in digestive processes and not only, now it’s the perfect moment to talk about a microorganism with a pretty interesting profile: Toxoplasma gondii.

Present in various percentages of populations across the world – in some areas even in about 84% of those living there – these microorganisms are thought to be responsible for the recklessness of some people. Studies also show that people who tend to be involved in traffic accidents are more likely to have these bacteria than those who like to play it safe.



These bacteria live in the mucous membrane of your respiratory tract, but it also exists in the digestive tract and vagina. Its pathogenic effects are often associated with influenza, and that’s what the bacteria are best known for. In extreme cases, it can even lead to meningitis, so its pathological manifestations are quite severe.

With up to 1,000 types of microorganisms living inside the human body, we are, without even knowing, the perfect environment for them to thrive. What we must remember is that we live in symbiosis with them and they are, for the most part, benign.



Ioana Moldovan

Ioana’s professional experience in the optics field has helped her understand the value of passing her knowledge forward. Her curious personality helps her gather useful information for her readers and her goal is to make technical information fun and accessible to everyone.

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