Probiotic Bacteria: What Are They?

The term "probiotic bacteria" (also known as good bacteria, friendly bacteria or beneficial bacteria) refers to the live bacterial organisms which live and work in our digestive tracts and which provide us with health benefits.

Rod shaped Lactobacillus acidophilus bacteria
Rod shaped Lactobacillus acidophilus bacteria

It may be a surprise to you that bacteria can indeed be beneficial to health. If you are like most people, you probably think of disease or grime when you hear the word bacteria. Probiotic bacteria are different! They have been shown to play a key role in keeping us healthy.

The phrase "probiotic bacteria" is often used to refer simply to the bacteria contained in probiotic supplements. However, we prefer to use the expression to refer to a wider definition of probiotic bacteria, which includes the naturally occurring probiotic bacteria which lives in our intestinal tracts as well as that which is found in fermented or probiotic foods.

What Do Probiotic Bacteria Do?

Probiotic bacteria are widely recognized as being key to good health. These wonderful communities of beneficial bacteria have been scientifically proven to1:

  • Assist with the digestion of food.

  • Produce many vitamins including B1 (thiamine), B2 (riboflavin), B3 (niacin), B5 (panthothenic acid), B6 pyridoxine, B9 (folic acid), B12 (cobalimine), vitamins A and K. Be aware though that not all probiotics produce the same nutrients. Some may produce a vitamin, whilst others may consume it. For example, the probiotic bacteria Lactobacillus bulgaricus produces vitamin B9 (folic acid) in yogurt whilst another beneficial bacteria, Lactobacillus acidophilus consumes it.

    Probiotic Bacteria Have Been Proven to Provide Health Benefits

  • Increase the availability of many minerals including copper, zinc, magnesium, iron, manganese and potassium.

  • Assist with the wave-like muscle contractions of the digestive tract, which move food through the system.

  • Break down toxins (directly and indirectly) using their secretions and colonization activities.

  • Promote anti-tumor and anti-cancer activity.

  • Enhance immune system responses and prevent infection2.

  • Reduce inflammation.

Additionally it is thought that probiotic bacteria may help reduce cholesterol levels though more research is needed in this area3.

Various probiotic bacteria are thought to help therapeutically with numerous conditions including pouchitis, constipation, food intolerance symptoms, colitis and Clostridium difficile (C. diff).

You should be aware though that many of the health benefits of probiotic bacteria are species specific. If for example you want to try probiotics for colitis, then be sure to select those specific species (e.g. Escherichia coli Nissle 1917, which is marketed as Mutaflor), which have been scientifically proven to help.

Remember that just like us, probiotic bacteria need food too! Ensure therefore that you choose foods which are rich in prebiotics as these will serve as an energy and growth source for your good or beneficial bacteria.

Where Exactly Do These Bacteria Live?

These bacteria live within us alongside much smaller numbers of archaea (single celled organisms with no nucleus) and eukarya (organisms with a nucleus), including fungi and protozoa. Together these organisms are known as the gut flora. Some of these organisms perform tasks that are helpful (probiotic) to human health, whilst others are harmful (pathobiotic). Eubiotic organisms also form part of this microbial community and these can be harmful or helpful depending on their location or colony size (Adams, 2009)4.

The large intestine is home to most of <br>the  bacteria that live in the human body.
The large intestine is home to most of the
bacteria that live in the human body

Most of these bacteria live in your colon or large intestine. Indeed scientific estimates suggest that the number of bacteria in the colon is between one hundred billion (1011) and one thousand billion (1012)!

Much lower numbers of probiotic bacteria inhabit your mouth (between approximately ten thousand and one billion (109) microorganisms per milliliter (ml) of saliva) and small intestine (circa ten thousand organisms per ml) and only a few bacteria are present in your stomach (around one thousand microorganisms per ml of contents). This is largely due to the fact that the stomach with its high acid concentration is a hostile environment to most bacteria.

The Balance of Digestive Flora

A healthy gut flora contains more probiotics (85%) than pathobiotics (15%) and thus the probiotics can keep the pathobiotics in check. Such a flora is also known as balanced flora and is considered a health asset. Conversely, an unhealthy flora has a dominance of pathobiotics and is said to be "unbalanced". Such a flora is associated with illness and the greater the flora imbalance the greater the dis-ease or symptoms of ill-health. Factors such as diet, lifestyle, age, stress and medication can all tip your gut flora towards "imbalance".

Dominant Species

There are many different species which live in our digestive tract and most of these are bacterial. Scientific estimates place the number of bacterial species to be between 3005 and 10006 with many estimates around 5007,8.. However, this area of research is in its infancy and it is still not possible to culture most of these bacteria. We therefore think that the actual numbers of bacteria in the digestive tract are likely to be much greater!

Although every person has a unique mix of organisms that make up their intestinal flora, some species of microorganism are more common and numerous than others. The key players in human gut flora are Lactobacillus and Bifidobacterium. There are many different species of these probiotic bacteria, which you can see in our list below:


  • Lactobacillus acidophilus
  • Lactobacillus brevis
  • Lactobacillus bulgaricus
  • Lactobacillus casei
  • Lactobacillus helveticus
  • Lactobacillus plantarum
  • Lactobacillus reuteri
  • Lactobacillus rhamnosus


  • Bifidobacterium bifidum
  • Bifidobacterium infantis
  • Bifidobacterium lactis
  • Bifidobacterium longum

You may at this point be wondering about the names of these bacteria. They are long and may seem confusing so just a short word on the names....

The word that appears first (in these cases Lactobacillus or Bifidobacteria) is the genus. Think of this as the bacterial clan or extended family name. Often this is abbreviated to simply L. or B.

The second word refers to the species of bacteria. It’s more specific than the genus9. Think of it as the surname or family name.

There’s also often a third name (often letters and/or numbers) attached to the end of the bacterial classification and you’ll frequently see this on the labels of probiotic supplements (e.g. Lactobacillus rhamnosus GG). This is more specific still and refers to the actual strain of probiotic within the species. Consider it like a first name.

If you would like to know more join us for our review of the above named strains of probiotic bacteria as well as our summary of the probiotic yeast Saccharomyces boulardii.


1.Adams, C.; Probiotics-Protection Against Infection; Sacred Earth Publishing; 2009; Delaware.

2.Reid G, et al; Potential uses of probiotics in clinical practice; Clin. Microbio; 2003; Rev. 16 (4): 658–72.

3.Ooi LG & Liong MT; Cholesterol-Lowering Effects of Probiotics and Prebiotics: a Review of In Vivo and In Vitro Findings; Int J Mol Sci.; June 2010 Jun; 11(6):2499-522.

4.Adams, C.; Probiotics-Protection Against Infection; Sacred Earth Publishing; 2009; Delaware.

5.Guarner F & Malagelada JR; Gut Flora in Health and Disease; Lancet 361 (9356): 512–9.

6.Sears CL; A Dynamic Partnership: Celebrating our Gut Flora; Anaerobe; October 2005; 11 (5): 247–51.

7.Steinhoff U; Who Controls the Crowd? New Findings and Old Questions about the Intestinal Microflora; Immunol. Lett; June 2005;. 99 (1): 12–6.

8.O'Hara AM & Shanahan F The Gut Flora as a Forgotten Organ".; EMBO Rep; July 2006;7 (7): 688–93.

9.The plural of genus is genera.

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