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What Are the Different Types of Bacteria in the Digestive System?

Debra Barnhart
Debra Barnhart

Bacteria in the digestive system number in the trillions, and most of these bacteria are referred to as friendly. Some experts say that friendly bacteria have a symbiotic relationship with their human hosts, because they help the human body in a variety of useful ways. Other types of bacteria in the digestive system are not so friendly, including those that produce cholera, botulism and salmonellosis.

Varying estimates indicate that there are 300 to 1,000 species of bacteria in the digestive system. In general, these bacteria, also known as gut flora, help the body in a number of ways that include aiding digestion, strengthening the immune system, and blocking the growth of unfriendly organisms. Friendly bacteria live mostly in the large intestine and part of the small intestine. The acidic environment of the stomach is not conducive to bacterial growth.

Friendly bacteria live mostly in the large and small intestine.
Friendly bacteria live mostly in the large and small intestine.

Bacteria begin to populate the human digestive system right after birth. One of the most common bacteria, according to experts, are Bacteroides. These bacteria aid in the digestion of plant food like spinach. Bacteroides release enzymes that the human body lacks, and by doing so the nutrients from plant foods can be absorbed. The human body gets vitamin K and some B vitamins due to the work of Bacteroides.

Trillions of bacteria live in a person's digestive system.
Trillions of bacteria live in a person's digestive system.

Lactobacillus is another type of friendly bacteria. Found in many food, such as yogurt, beer, wine and chocolate, Lactobacillus bacteria have a reputation for helping the immune system and fending off diseases like the flu. Some research seems to indicate that Lactobacillus has cancer-fighting properties as well. Lactobacillus has been shown to inhibit tumor growth when given to animals.

Some bacteria in the digestive system have a reputation for being very unfriendly and wreaking a lot of havoc. Examples include Vibrio cholera, Clostridium botulinum and several types of Salmonella bacteria. The diseases caused by these bacteria may sometimes be deadly.

Vibrio cholera, the source of cholera, can be spread through drinking water. Its symptoms include diarrhea and dehydration, with severe dehydration being one of the most common causes of death from this disease. Clostridium botulinum produces the very deadly disease botulism by releasing toxins that can initiate muscle paralysis, blurred vision and respiratory distress in addition to diarrhea and vomiting. Salmonella poisoning causes vomiting and diarrhea, which occurs from eating infected eggs, meat and processed foods. This bacteria produces a disease that is self-limiting, meaning the body will usually fight off the disease on its own.

Discussion Comments


@David09 - You better watch your beef and chicken too. They’ve been responsible for salmonella outbreaks from time to time. We can’t bury our heads in the sand about these issues but we can’t live in total paranoia either. The best thing to do is to cook your food as much as possible to kill any bacteria and hope for the best.


@miriam98 - I generally make it a point to avoid drinking tap water in my house, despite assurances to the contrary telling me the stuff is safe.

Yeah, it’s been tested and we have certain environmental regulations that ensure a certain level of purity as regards particulate matter and so forth.

Still, I don’t trust it. I only drink distilled or filtered water. I actually think reverse osmosis is the best process to ensure that I get nothing but pure H20, free of bad bacteria.


@Charred - I can’t say that I know of any science that will back you up, however I do share some of your skepticism about tablets, especially the herbal kind. Too often you don’t really know what’s in those tablets, and of course the FDA doesn’t regulate that stuff.

So it’s always a shot in the dark in my opinion. As for me, however, I do prefer food sources for my good bacteria. I remember it was Hippocrates that said, “Let your medicine be your food, and your food your medicine.”

For example, I have always known that wine and chocolate were good for you. They have antioxidants and so were recommended for people with heart conditions.

I’ve always had some red wine with an evening meal and a dark chocolate here or there. I am pleased to discover that these foods deliver good bacteria to my system as well. That’s killing two birds with one stone.


I don’t have any scientific basis to back this up, but I believe that it’s better to get your “good bacteria” through living cultures like yogurt instead of through supplements.

Again, I don’t know that it’s accurate one way or the other but I just feel like I am getting a “direct injection” with yogurt rather than swallowing a tablet and waiting for it to dissolve in my stomach. Does anyone have any opinions on this?

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    • Friendly bacteria live mostly in the large and small intestine.
      By: nerthuz
      Friendly bacteria live mostly in the large and small intestine.
    • Trillions of bacteria live in a person's digestive system.
      By: maya2008
      Trillions of bacteria live in a person's digestive system.