What is Lactobacillus?

Lactobacillus is a type of probiotic 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 actually a species of bacteria from the Lactobacillus genus (plural Lactobacilli), a widely used type of friendly bacteria often found in probiotic supplements

In this article we look at:

What kind of probiotic is Lactobacillus?

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

Lactobacillus taxonomy diagram

All probiotics 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 probiotic 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 probiotics 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, promote plant growth, and prevent disease in plants1.

What are the benefits 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 provide their ‘hosts’ with many health benefits.

It’s difficult to pinpoint the functions of the Lactobacillus genus, as all Lactobacilli will have some benefits 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 benefits are unique to the individual species and strains. Strains from this genus have been extensively researched and found to offer health benefits for a variety of conditions including:

  • Loose stools: the strains Lactobacillus acidophilus NCFM ® and Lactobacillus rhamnosus GG ® are two of the most researched probiotics in the world. They have shown great promise for the support of occasional diarrhoea and loose stools arising from a variety of different causes3.
  • IBS and bloating:  Lactobacillus acidophilus NCFM® is the most extensively researched strain of L. acidophilus in the world. One of its strengths is for the support of generalised IBS symptoms, especially bloating4. Lactobacillus acidophilus Rosell-52 is another highly researched Lactobacillus strain which has shown consistently solid results for IBS and gut support5.
  • Mental health and wellbeing: As well as being a great all-rounder for supporting gut health, Lactobacillus acidophilus Rosell-52 has been researched for its potential in the support of mental health and wellbeing6.
  • Immune support: Some strains of Lactobacilli have shown particular promise for the support of immune health. Lactobacillus paracasei CASEI 431® has been extensively researched and found to shorten the duration of cold and flu symptoms7.
  • Vaginal health: Lactobacillus rhamnosus GR1® is a strain of probiotic bacteria from the Lactobacillus genus that prefers to live in the genito-urinary tract. It has been proven in numerous studies to help support female intimate health, especially in the support of vaginal and urinary tract infections 8,9.

Which is the best Lactobacillus probiotic supplement?

As explained above, different Lactobacillus strains have different properties, so the best Lactobacillus supplement for you will be the one which contains strains researched for the health conditions you wish to support. So, first look for Lactobacillus probiotics 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 probiotics 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 – you should be able to find related research.
  • 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).

For more information, read microbiologist Dr. Kate Stephens’ article about how to choose a high-quality supplement.

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

Some people worry whether Lactobacillus can be harmful; however, taking probiotics in supplement form is considered very safe, and side effects from taking Lactobacillus probiotic 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 probiotic 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 can be found in various dietary sources. Find out 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 wish to read about other live bacteria genus, including 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.
  3. Ruiz-Palacios G. et al., (1996). ‘Feeding of a probiotic for the prevention of community acquired diarrhea in young Mexican children’. Pediatric Research, 39 (Pt. 2):104, Abstr. #1089.
  4. Faber, S.M., (2000). ‘Treatment of abnormal gut flora improves symptoms in patients with irritable bowel syndrome’. American Journal of Gastroenterology, 95(9):2533.
  5. Benes Z. et al., (2006), ‘Lacidofil (Lb. acidophilus Rosell-52 and Lb. rhamnosus Rosell-11) alleviates the symptoms of IBS’. Nutrafoods, 5:20-27.
  6. Messaoudi M. et al., (2011), ‘Assessment of psychotropic-like properties of a probiotic formulation (Lactobacillus helveticus R0052 and Bifidobacterium longum R0175) in rats and human subjects’. British Journal of Nutrition, 105(5):755.
  7. Jespersen L. et al., (2015), ‘Effect of Lactobacillus paracasei subsp. paracasei, L. casei 431® on immune response to influenza vaccination and upper respiratory tract infections in healthy adult volunteers: a randomized, double- blind, placebo-controlled, parallel-group study’. Am.J.Clin.Nutr., 101:1188-1196.
  8. Vujic et al., (2013), ‘Efficacy of orally applied probiotic capsules for bacterial vaginosis and other vaginal infections: a double-blind, randomized, placebo-controlled study’. Eur. J. Obstet. Gynecol. Reprod. Biol., 168(1): 75-9.
  9. Beerepoot et al., (2012), ‘Lactobacilli vs antibiotics to prevent urinary tract infections: a randomized, double-blind, noninferiority trial in postmenopausal women’. Arch. Intern. Med., 172(9):704-12.