What is Lactobacillus?

Lactobacillus is a type of friendly bacteria often found in the gut or urinary tract. Find out more about Lactobacillus in this FAQ.

If you’ve heard of ‘acidophilus’, then you’ve probably heard of Lactobacillus. But L. acidophilus is a actually a species of bacteria from the Lactobacillus genus (plural Lactobacilli), a widely used type of friendly bacteria often found live cultures supplements.  

In this article we look at:

What kind of good bacteria is Lactobacillus?

The name ‘Lactobacillus’ is very well-known; in fact many people call all live cultures Lactobacillus as a generic term. But Lactobacillus is actually the name for a particular genus of lactic-acid-producing bacteria (hence the name Lactobacillus). A genus is a ‘family’ of bacteria. Within the Lactobacillus genus, there are numerous well-known friendly bacteria species, including Lactobacillus reuteri, Lactobacillus rhamnosus, and Lactobacillus acidophilus. The Lactobacillus genus contains some of the world’s most highly researched live cultures which have been featured in countless clinical trials. One such strain is Lactobacillus acidophilus NCFM®, the most extensively researched strain of Lactobacillus acidophilus in the world.

Lactobacillus taxonomy diagram

All bacteria from the Lactobacillus genus share certain qualities, but it is important to note that within the numerous species of Lactobacilli, there are many different strains. Each bacterial strain will have its own unique modes of action in the body. Therefore, when considering a live cultures supplement, it is best to compare them at strain level rather than just by genus or species. This way you can ensure you are getting the right types of friendly bacteria to suit you.

Read this page to find out more about the difference between species and strains of bacteria.

Where is Lactobacillus found?

Lactobacilli are ubiquitous in nature and can be found living in a wide variety of environments. In animals and humans, they are natural residents of the intestines, and also like to inhabit the human vagina and oral cavity. They are also found in soil (most commonly associated with the rhizosphere), and in plants (particularly decaying plant material). They have been used in agriculture for years to improve soil quality, and promote plant health and growth.1

What are the functions of Lactobacillus?

This genus of bacteria is very well-known, but many people are still unclear about what Lactobacillus does. Most people want to know ‘are Lactobacilli good bacteria?’, and the answer to this is ‘yes’! These bacteria live in harmony with their ‘hosts’.

It’s difficult to pinpoint the functions of the Lactobacillus genus, as all Lactobacilli will have some properties in common, such as their ability to produce acids, including lactic acid. Many species and strains of Lactobacilli can colonise in the gut or vaginal microbiomes2, where they improve the environment by producing bacteriocins (natural antimicrobial agents), which inhibit the growth of pathogens (undesirable micro-organisms). However, many properties are unique to the individual species and strains.

Which is the best Lactobacillus supplement?

As explained above, each Lactobacillus strain will have different properties, so the best Lactobacillus supplement for you will be the one which contains strains that suit your individual needs. Therefore, first look for Lactobacillus supplements which provide the strain names.

As well as finding a supplement which contains the best strain for your needs, there are also a few other key points to consider when choosing Lactobacillus friendly bacteria to ensure you choose a high-quality supplement:

  • The Lactobacillus strain should have sufficient scientific evidence to support its safety and survival to the gut. Search for the strain online to see the research which supports it.
  • Don’t be drawn in by huge billion counts. Higher billions do not necessarily equal higher quality – it’s much more important to get the right strains, even if they’re in lower quantities.
  • Check it has a ‘time of expiry’ guarantee as opposed to a ‘time of manufacture’ guarantee, as this means the contents are guaranteed until the supplement goes out of date, rather than just at the time of manufacture (as numbers can decrease after this point).

Luckily for you, Optibac friendly bacteria supplements satisfy all of the above criteria! The following Optibac supplements contain Lactobacillus friendly bacteria:

Some people worry whether Lactobacillus can be harmful; however, rest assured, taking live cultures in supplement form is considered very safe, and side effects from taking Lactobacillus friendly bacteria are rare. Mild symptoms such as abdominal bloating and/or gas may occasionally be caused as a direct result of the positive ‘shift’ in the microbiota towards a healthier balance of gut microbes.

See this FAQ about side effects for more information.

probiotic capsule
Lactobacillus bacteria are often used in live cultures supplements 

Which foods contain Lactobacillus?

It’s hard to say what is the best source of Lactobacillus, as the resourceful species and strains from this genus are found in various dietary sources. Read more about fermented foods over on the Probiotics Learning Lab.

Lactobacillus bacteria can ferment the milk-sugar lactose, so are very at home in dairy products. For this reason, strains of Lactobacilli are used commercially to ferment a variety of dairy products including cheese, yoghurt, and kefir. But these versatile bacteria are equally at home when fermenting vegan cheeses, vegetables such as cabbage in sauerkraut and kimchi, and grains in fermentation for sourdough bread production. Lactobacillus strains can also be found in various types of pickles, and preserved foods like olives.

In addition to these Lactobacillus foods, the bacteria are also used in live cultures supplements in various different formats, including Lactobacillus tablets, capsules, sachets, chewable products, and liquids.

Further reading:

Healthcare practitioners might be interested to find out more about Lactobacillus on the Probiotics Database, on the Probiotic Professionals site. 

Some species of Lactobacilli have recently been reclassified. For more information about this, read Dr. Kate’s article about the new Lactobacillus names.

You may also like to read about another friendly bacteria genus in our FAQ What is Bifidobacterium?

Author: Dr Kate Stephens PhD (Food and Microbial Sciences) BSc(Hons) Medical Microbiology


  1. Lamont, J.R. et al, (2017) From yogurt to yield: Potential applications of lactic acid bacteria in plant production, Soil Biology and Biochemistry, Volume 111:1-9 ISSN 0038-0717
  2. DebMandal, M. et al (2012) Detection of intestinal colonization of probiotic Lactobacillus rhamnosus by stool culture in modified selective media. Asian Pacific Journal of Tropical Disease 205-210.