What is Friendly Bacteria?

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  • Written By: Mary McMahon
  • Edited By: O. Wallace
  • Last Modified Date: 20 October 2019
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Friendly bacteria, also known as probiotic or commensal bacteria, are bacteria which confer some sort of positive health benefit on their host. These bacteria live on or in the body of their host, and in some cases, they are actually critical to well-being. Scientists are constantly learning more about these bacteria and their functions in the body, and they've made some surprising discoveries about the ways in which these bacteria work.

One of the most famous groups of friendly bacteria is the bacteria found in the gut. Numerous species of bacteria line the gut to take advantage of the ample supplies of food which move through the gut on a daily basis. In the process of breaking food down to access valuable nutrients, the bacteria also help the body digest various foods, thereby increasing the amount of nutrition that the body can extract from food. Probiotic bacteria in the gut also combat bacterial invaders which can cause infection.

Friendly bacteria can also be found in the mouth, cutting down on the risk of infection from bacteria and viruses which enter the mouth, and in the linings of other mucus membranes. The skin hosts large numbers of good bacteria which digest the waste products secreted by the skin.


There are a number of ways in which the balance of friendly bacteria in the body can be disrupted. The use of antibiotics to address infections can kill some commensal bacteria along the way, since antibiotics are not always very selective. Health conditions can also lead to an imbalance, such as a flourishing of a bacterial species which is normally only present in small numbers.

Sometimes, commensal bacteria may be deliberately introduced to the body to help the body cope with an imbalance. While this practice was once confined to practitioners of alternative medicine, it has since caught on among regular medical practitioners, who may consider the recommendation of probiotic supplements to patients with certain conditions. Experimental procedures have also involved the use of good bacteria as an alternative to antibiotics, with the friendly bacteria knocking out bacterial infections. Lactobacillus, for example, a commensal bacteria found in yogurt, appears to be effective at preventing oral infections.

Probiotics can be added to the body through the use of tablets and supplements which contain cultured probiotics, and also through the consumption of cultured foods with cultures which are left alive, rather than being neutralized by a pasteurization process. Yogurt and cheese are two common cultured foods which are easy to add to the diet. People should not attempt to treat a medical condition with friendly bacteria without consulting a doctor.


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Post 3

What are some friendly bacteria foods? I know of course about probiotic yogurt, and I've read that some cheeses have good bacteria (and fungus, for that matter), but what are some other good sources of friendly bacteria?

Post 2

What does it mean when a bacteria cell is gram negative? Does that mean that it's a good bacteria? And since there are good bacteria species, do fungus species have "good" and "bad" species too?

Post 1

I'm so glad that you wrote this article about good bacteria. Although there are a lot of bad bacteria out there -- e. coli and streptococcus bacteria come to mind -- there really are a lot of friendly bacteria as well.

I will definitely be using this in my bacteria characteristics lesson next quarter. All kids hear about is killing bacteria and getting rid of bacteria, so they have no idea that some bacteria is actually good for you!

Thanks so much for this information and a well-written article.

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