Bacterial Spotlight: All About Lactobacillus

What is Lactobacillus?

Lactobacillus is a group of lactic acid bacteria that live in fermented foods, the mouth, the small intestine, and the vagina. In the adult colon, they make up a small share of the community, often below 1%. Humans have eaten them for thousands of years in yogurt, cheese, kimchi, and pickles, which is why they are among the most common bacteria in probiotic foods and supplements.

The origins of Lactobacillus

Lactobacilli are rod-shaped bacteria that turn sugars into lactic acid, which gives the group its name. Most tolerate oxygen and thrive in acidic conditions, which suits them to the stomach, the small intestine, and fermenting foods. In 1900, paediatrician Ernst Moro isolated one from infant stool. A few years later, Ellie Metchnikoff linked the lactic acid bacteria in Bulgarian yoghurt to long life, an idea that helped launch the modern probiotic industry.

What does Lactobacillus do

The functions below are shared across most of the genus. Specific species and strains vary in how strongly they carry each one.

They turn sugars into lactic acid. Even though some species produce mainly lactic acid, others also produce acetate, ethanol, and carbon dioxide. These are acidic and lowers pH, which makes the gut less hospitable to many pathogens (and also how it preserve foods like yoghurt and kimchi!).
They feed other beneficial bacteria. The lactate and acetate produced by lactobacillus can be taken up by other gut bacteria, and converted into short-chain fatty acids, in what we call cross-feeding. What each lactobacillus releases depends on how it ferments sugars
Homofermentative process by L. acidophilus, L. gasseri, L. delbrueckii subsp. Bulgaricus produces lactate.
Heterofermentive process by Limosilactobacillus reuteri, Limosilactobacillus fermentum, Levilactobacillus brevis produces lactate, acetate, ethanol, and carbon dioxide.
Facultatively heterofermentative process by Lacticaseibacillus rhamnosus, Lactiplantibacillus plantarum produces mainly lactate, with acetate from some sugars.

These outputs then feed three groups of gut bacteria:

Lactate to butyrate: Anaerobutyricum hallii and Anaerostipes species combine lactate with acetate to make butyrate.
Lactate to propionate: Veillonella species and Coprococcus catus convert lactate into propionate.
Acetate to butyrate: Faecalibacterium prausnitzii and Roseburia species use acetate to make butyrate.

Butyrate is the main energy source for the cells lining your colon, and a well-nourished lining forms a tighter barrier between your gut contents and bloodstream. Propionate travels to the liver, where it is involved in regulating glucose production.

They produce antimicrobial compounds. Some strains also produce bacteriocins, which are small proteins that target competing bacteria. These help lactobacilli compete for space and nutrients from other bacteria, including pathogens, to establish itself in the gut. At the moment, most of this evidence comes from laboratory results.
They modify bile acids. Bile acids are released by your liver to breakdown fat into small droplets. Many lactobacilli work with other bacteria to turn it into secondary bile acids, which help keep harmful bacteria in check. They also act as messengers to help regulate cholesterol, blood sugar, and fat metabolism.
They produce neuroactive compounds. Certain strains like produce GABA, which is a messenger signalling molecule used by the nervous system. Even though these molecules do not reach the brain directly, they are able to signal to the brain through the vagus nerve, one of the several ways your gut is linked to your brain.

For the curious: sticky pili. Lacticaseibacillus rhamnosus GG, one of the most studied probiotic strains, has hair-like structures called pili on its surface. Their tips carry a mucus-binding protein that lets the strain attach to the gut lining. Like most probiotics, it still fades after you stop taking it.

What affects your levels of Bifidobacteria

Birth method. Lactobacilli usually dominate the vaginal microbiome, so babies born vaginally pick them up at birth. Babies born by caesarean section start with more skin-associated bacteria.
Diet. Much of the Lactobacilli found in adult stool comes from food. People who eat fermented foods regularly tend to have higher levels, though many of these bacteria are just passing through.
Stomach acids. People taking proton pump inhibitors (a common stomach acid medication) tend to have more lactobacilli in their stool because lower stomach acid lets more bacteria from the mouth and food survive.
Antibiotics. Conversely, lactobacilli are sensitive to common antibiotics and drop during treatment.

How to increase Bifidobacteria naturally

Eat fermented foods

Fermented foods are the most direct source of lactobacilli. In a Stanford trial, a diet high in fermented foods increased overall microbial diversity and lowered several markers of inflammation over 10 weeks. Good sources include

Yoghurt and kefir with live cultures
Kimchi and sauerkraut
Vegetables pickled by fermentation in brine

Tip: Check the label for ‘live’ or ‘active’ cultures. Pasteurised products and vinegar-based pickles no longer contain live bacteria.

Eat probiotic fibres

A meta-analysis of fibre trials in healthy adults found that fibre supplementation increased both Lactobacillus and Bifidobacterium. Onions, garlic, leek, asparagus, legumes, and whole grains are rich sources.

Tip: Increase gradually to limit gas and bloating.

Add polyphenol-rich foods

Polyphenols are plant compounds found in cocoa, tea, berries and other fruits and vegetables. Most pass through to the colon, where gut bacteria break them down. In a four-week trial, a high-flavanol cocoa drink increased Bifidobacteria with lactobacilli. This is a less established approach than fibre, but it adds to the case for a varied, plant-rich diet.

Consider probiotics

Most Lactobacillus supplements contain strains that do no settle in the gut permanently. They are detectable while you take them, but deplete when you top so effects depend on regular use.

Tip: Choose products that name specific strains to ensure quality.

Use antibiotics only when you need them

Antibiotics reduce many gut bacteria, including Lactobacilli. Most species recover within weeks, though some can stay absent for months. Take antibiotics only when a doctor prescribes them, and complete the course as instructed. Afterwards, a fibre-rich diet gives recovering bacteria what they need to regrow.

Be consistent

Your gut bacteria respond to what you eat over months, and gains from prebiotics tend to fade when you stop. How much you respond may also depend on which bacteria you already have. In a Stanford trial, participants' microbiomes responded differently to a high-fibre diet depending on their starting composition. A gut microbiome test can show where you're starting from.

Why the strain name matters

Each species occupies its own niche, and the clinical research is specific to individual species and strains. Two strains of the same species can behave differently in the body, so clinical results for one strain don't carry over to another. When you compare products, look for the full strain code on the label.

A new era for Lactobacilli

2020 reclassification adds a complication: the same strain may appear under its old name in older research and its new name on current labels. For example, Lacticaseibacillus rhamnosus GG (ATCC 53103) appears as Lactobacillus rhamnosus GG in most studies before 2020.

Lactobacillus rhamnosus is now Lacticaseibacillus rhamnosus
Lactobacillus casei is now Lacticaseibacillus casei
Lactobacillus plantarum is now Lactiplantibacillus plantarum
Lactobacillus reuteri is now Limosilactobacillus reuteri
Lactobacillus fermentum is now Limosilactobacillus fermentum
Lactobacillus salivarius is now Ligilactobacillus salivarius
Lactobacillus brevis is now Levilactobacillus brevis
Lactobacillus acidophilus and Lactobacillus gasseri remain unchanged

How do I know if I have enough Lactobacilli?

You can’t tell if you have enough of it from how you feel. A gut microbiome test, which analyses the bacteria in your stool sample, is one way you can measure your levels.

Lactobacilli are naturally a small part of the adult gut, so a low or undetectable reading in a gut microbiome test is common in healthy people. A stool test also reflects the colon more than the small intestine, where lactobacilli are more abundant.

More importantly, the level of a single group of bacteria tells you little on its one. Your gut microbiome works as a community, where Lactobacilliu pass lactate to butyrate produces, and start bile acid transformation that other bacteria complete. Many of their jobs are shared with other species, so a well-populated, diverse community goes further than a single low read for Lactobacilli.

Since your gut microbiome is impacted by your diet and lifestyle, It is important that your results are compared with to microbiomes who look like yours so that you get an accurate picture of what’s supposed to be typical for you. Your gut microbiome results should also be read as part of a wider picture, together with your health history so that you can decide if there is anything that requires further attention.

Frequently asked questions

What are lactobacilli?
They are lactic acid bacteria that live in fermented foods, the mouth, the small intestine, and the vagina. They make up a small share of the adult colon.
Are Lactobacilli good for you?
Many strains are widely considered beneficial and have a long history of safe use in food. Probiotic use in premature infants or people with weakened immune systems should be under medical supervision.
How can I increase my Lactobacilli?
Eat fermented foods with live cultures, such as yoghurt, kefir, and kimchi, alongside prebiotics fibres from onions, garlics, legumes, and whole grains.
Which Bifidobacterium species is best?
It depends on what you want to support. Benefits in clinical studies are specific to individual strains, so the strain named on the label matters most.
What is the difference between Bifidobacterium and Lactobacillus?
Both are used widely in probiotics. Bifidobacteria live mainly in the large intestine and dominate the infant gut. Lactobacilli are lactic acid producers found through the gut and in fermented foods such as yoghurt. In 2020, the Lactobacillus group was reclassified into 25 genera, so many familiar strains now carry new names, such as Lacticaseibacillus rhamnosus.
What is the Lactobacillus in Yakult?
Yakult contains Lacticaseibacillus paracasei strain Shirota, formerly known as Lactobacillus casei Shirota. It was isolated in Japan in 1930 by Dr Minoru Shirota and is one of the most studied probiotic strains. Like most probiotic strains, it passes through the gut and fades after you stop drinking it.
How does Lactobacillus survive stomach acid?
Stomach acid kills many bacteria, and survival varies widely between strains. Lactobacilli have an advantage because they produce acid themselves and are adapted to acidic environments. Some strains pump excess acid out of their cells, and others neutralise it using amino acids. Food also helps, since a meal raises stomach pH and dairy buffers acid further. Once past the stomach, lactobacilli face bile in the small intestine, where the bile salt hydrolase enzyme helps some strains cope. Supplements often use capsules designed to protect bacteria during this journey.
What temperature kills Lactobacillus?
Most lactobacilli grow best at around body temperature, between 30°C and 40°C. Some yoghurt strains tolerate up to about 45°C. Above roughly 50°C, most start to die, and pasteurisation or cooking kills nearly all of them. To keep the bacteria alive, add fermented foods such as kimchi or yoghurt after cooking rather than heating them. Cooked dishes like kimchi stew still offer fibre and flavour, without live cultures. For supplements, follow the storage instructions on the label, as heat and humidity reduce the number of live bacteria over time.

This article is for general information and isn't a substitute for personalised medical advice. If you have ongoing gut symptoms, speak with a doctor.

Last updated: 27 September

About the author

Yuzu Tay holds a bachelor's in biomedical engineering and writes on the science behind the latest in healthcare, translating clinical research into practical guidance. Her past work spans cancer companion diagnostics, liver fibrosis, and gut health.

Glossary

Acetate: A short-chain fatty acid made when bacteria ferment sugars and fibre. Other gut bacteria use it to make butyrate.
Bacteriocin: A small protein made by some bacteria to target competing bacteria.
Bile acids: Compounds made by the liver from cholesterol and released into the small intestine to help digest fat. They also act as messengers that help regulate metabolism.
Butyrate: A short-chain fatty acid and the main energy source for cells lining the colon.
Cross-feeding: When one type of bacteria uses compounds released by another as food.
Fermentation: The process bacteria use to break down sugars and fibre without oxygen, producing acids, gases and other compounds.
Flavanols: A type of polyphenol found in cocoa, tea and some fruits.
GABA (gamma-aminobutyric acid): A messenger molecule used by the nervous system. Some gut bacteria produce it.
Lactate (lactic acid): The main product of lactobacilli fermentation. It lowers pH and feeds other gut bacteria.
Microbiome: The community of microorganisms living in a particular environment, such as the gut.
Microbial diversity: The range of different bacteria in the gut. Higher diversity is associated with better gut and metabolic health.
Pasteurisation: Heating food or drink to kill microorganisms, including beneficial live cultures.
Pathogen: A microorganism that can cause disease.
Polyphenols: Plant compounds found in cocoa, tea, berries and other fruits and vegetables. Gut bacteria break most of them down in the colon.
Prebiotic: A food component, usually a fibre, that feeds beneficial gut bacteria.
Probiotic: Live microorganisms that provide a health benefit when consumed in adequate amounts.
Propionate: A short-chain fatty acid that travels to the liver and is involved in regulating glucose production.
Proton pump inhibitor (PPI): A common medication that reduces stomach acid.
Secondary bile acids: Bile acids transformed by gut bacteria. They help keep harmful bacteria in check and act as metabolic messengers.
Short-chain fatty acids (SCFAs): Compounds such as acetate, propionate and butyrate, produced when gut bacteria ferment fibre.
Species: A specific type of bacteria within a genus, such as Lactobacillus acidophilus.
Strain: A specific variant within a species, identified by a code such as GG or ATCC 53103. Clinical results apply to the strain tested.
Vagus nerve: A major nerve connecting the gut and the brain.

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Bacterial Spotlight: All about Lactobacillus