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Unlocking the Secrets of Lactobacillus: A Comprehensive Guide to Testing Patient Levels and Deciphering High and Low Levels

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Unlocking the Secrets of Lactobacillus: A Comprehensive Guide to Testing Patient Levels and Deciphering High and Low Levels

Lactobacillus is a genus of beneficial bacteria found in the human gut, mouth, vagina, and certain foods. Healthy levels of these good bacteria within the human microbiome help with digestion, absorption, infection prevention, and overall well-being. This article will discuss some of the most well-researched Lactobacillus species and their health benefits. Understanding the specific indications of probiotic species and strains is required for appropriate supplementation and meeting health goals.


What is Lactobacillus spp.?

There are over 200 species of Lactobacillus, a bacteria of the Firmicutes phylum. Many species and strains are commensal organisms of the human microbiome and are found in probiotic supplements and fermented foods. There are numerous studies on the therapeutic effects of Lactobacillus, including the formation of lactic acid, inhibition of pathogenic colonization, enhancement of the intestinal barrier integrity, production of B vitamins and short-chain fatty acids, and modulation of the immune system. (1)

What Are the Main Lactobacillus Species: What Are Their Health Benefits?

Below outlines and summarizes health benefits associated with the main Lactobacillus species.

Lactobacillus acidophilus

Lactobacillus acidophilus (L. acidophilus) is a good bacteria in the human oral, pulmonary (lungs), gastrointestinal, and genitourinary microbiomes. Supplementally, L. acidophilus is added to many probiotics in capsule, tablet, wafer, powder, and suppository form. Additionally, L. acidophilus is commercially added to many foods; it is used as a live culture in up to 80% of commercially-made yogurt in the United States. (2)


L. acidophilus has been shown to effectively treat various types of diarrhea, including acute diarrhea caused by bacterial or viral infection, chronic diarrhea, and antibiotic-induced diarrhea (2).

Irritable Bowel Syndrome

Supplementation with L. acidophilus probiotics has improved abdominal pain and bloating in patients with irritable bowel syndrome (IBS) after 1-2 months.

Vaginal Infections

Lactobacilli are the most predominant type of bacteria in the vagina, producing lactic acid to prevent the growth of harmful bacteria. Reductions in Lactobacilli can predispose an individual to bacterial vaginosis (BV) and vulvovaginal candidiasis. Oral and intravaginal administration of L. acidophilus can assist in treating these infections and reduce associated vaginal inflammation. (3, 4)


Eczema, or atopic dermatitis, is a dermatologic condition that causes dry, itchy, and inflamed skin. Eczema commonly presents itself in infancy, and dysbiosis is known to be a contributing factor to its development. One study has shown that probiotic administration containing L. acidophilus to pregnant women and their infants during the first three months of life reduced eczema prevalence in infants by 22%.

Lactobacillus brevis

Lactobacillus brevis (L. brevis) is commonly isolated from dairy products, fermented foods, and the intestinal and vaginal microbiomes. L. brevis is particularly beneficial for the stomach, inhibiting the growth of Helicobacter pylori infection and, in doing so, preventing stomach ulcers.

Lactobacillus casei

Lactobacillus casei (L. casei) is used in many probiotic formulations and has been shown to provide many health benefits, from digestive function to cancer prevention.

Digestive Health

The ability to produce antimicrobial substances, enhance the epithelial barrier, compete for pathogenic binding sites, and modulate the immune system are all likely mechanisms by which L. casei supports digestive health and function. Research has shown benefits in treating colitis, antibiotic-associated diarrhea, and H. pylori infection with L. casei probiotics. (5, 6)


Children colonized with L. casei have a reduced risk of developing allergic diseases, like atopic dermatitis and asthma, by age five (5).


Preliminary research has shown promising results in using L. casei probiotics in treating colorectal cancer. Additionally, probiotic therapy can improve side effects caused by cancer treatments, such as diarrhea and abdominal discomfort. (5)

Metabolic Disease

L. casei in the gut microbiome is associated with reduced rates of obesity. The ability of L. casei to modulate the immune system to reduce inflammation, along with its influence over insulin sensitivity, supports healthy weight and blood glucose control. (5, 7)

Lactobacillus delbrueckii subsp. bulgaricus and lactis

These two species of Lactobacillus are largely used in the dairy industry for cheese and yogurt production. By modulating T cells of the immune system, L. delbrueckii enhances systemic immunity and has been used in treating inflammatory bowel disease (IBD), liver disease, and periodontal disease. (8)

Lactobacillus fermentum

Because of its ability to produce antimicrobial peptides, the Lactobacillus fermentum (L. fermentum) has extended beyond human health and into food preservation. L. fermentum has been associated with improved immune function, prevention of gastrointestinal and respiratory infections, reduction of systemic cholesterol levels, and prevention of alcoholic liver disease and colorectal cancer. (9)

Lactobacillus gasseri

Lactobacillus gasseri is beneficial in treating many digestive and vaginal disorders.

Digestive Health

Research has shown the use of L. gasseri probiotics beneficial in preventing and treating peptic ulcers, H. pylori infection, acute diarrhea, ulcerative colitis, and IBS. (10, 11)

Vaginal Health

L. gasseri is a well-documented species within the vaginal microbiome that confers a protective effect against infection, such as BV. Its antimicrobial properties appear especially effective against Gardnerella vaginalis and Prevotella bivia, both associated with BV infection. (10, 12)

Weight Loss

Several clinical trials have shown that supplementation of L. gasseri has resulted in up to 8.5% reduction in visceral fat mass in adults with obesity. (13, 14)

Lactobacillus helveticus

Lactobacillus helveticus (L. helveticus) is found naturally in the gut and certain foods like cheese, milk, and fermented vegetables. L. helveticus has been linked to improved gastrointestinal, oral, and mental health.

Gastrointestinal Health

Consumption of L. helveticus probiotics promotes butyrate production, a short-chain fatty acid that confers many benefits to the gastrointestinal tract and systemic function. L. helveticus can modulate host immune responses and enhance protection against pathogens, preventing gastrointestinal infections. Other digestive benefits provided by L. helveticus include improving food tolerance by removing allergen proteins from foods and enhancing the bioavailability of nutrients. (15)

Mental Health

L. helveticus increases serotonin, norepinephrine, and brain-derived neurotrophic factor levels in the brain, which are associated with reduced anxiety, depression, and cognitive dysfunction. Additionally, one study that gave elderly subjects fermented milk with L. helveticus improved sleep quality and quantity. Good quality sleep is known to reduce physiologic stress and improve mood. (16)

Lactobacillus paracasei

Lactobacillus paracasei (L. paracasei) is found in the mouth and intestinal tract, as well as in dairy products and fermented vegetables.

Infections and Immune Function

L. paracasei has been found to support the immune system, reducing illness rates in children attending daycare and inhibiting the growth of pathogenic bacteria, including E. coli and Salmonella. In part, the ability to prevent infection comes from L. paracasei's ability to stimulate the immune system and cytokine secretion. (17, 18)


L. paracasei strains are resistant to heat and intestinal enzyme degradation, making it a common species in probiotic digestive formulas. Its anti-inflammatory properties, ability to promote the growth of Bifidobacterium spp., and enhancement of short-chain fatty acid production all support health, gastrointestinal health, and digestive function. (18)

Lactobacillus plantarum

Lactobacillus plantarum (L. plantarum) can bind to the intestinal mucosa, increase the population of healthy bacteria within the microbiome, and confer anti-inflammatory properties to the host. Because of this, L. plantarum has been shown to improve pain and bloating in patients with IBS and skin symptoms in children with eczema.

A healthy population of L. plantarum within the microbiome may also support metabolic health, improving physical performance, maintaining a healthy weight, and reducing blood pressure (19).

Lactobacillus reuteri

Lactobacillus reuteri (L. reuteri) can influence the immune system and has strong anti-inflammatory effects. L. reuteri upregulates the production of regulatory T (Treg) cells, suppressing inflammation and promoting self-tolerance.

L. reuteri can improve digestive function and reduce gastrointestinal symptoms, including colic and constipation (20, 21). It is also a predominant species within the vaginal microbiome and can be used orally or intravaginally to treat BV.

Lactobacillus rhamnosus

Lactobacillus rhamnosus (L. rhamnosus) is found in the intestines and vagina and is commonly added to dairy products. Many studies support its many health benefits and use in treating various conditions.

Digestive Health

L. rhamnosus has been shown to prevent the overgrowth of opportunistic and pathogenic microorganisms within the digestive tract and encourage the growth of other beneficial bacterial strains. L. rhamnosus increases the production of short-chain fatty acids and prevents intestinal barrier dysfunction, which can improve IBS symptoms. Additionally, supplementing L. rhamnosus during antibiotic therapy can reduce the risk of antibiotic-associated diarrhea from 22.4% to 12.3%. (22-24)


Several studies have shown reductions in oral bacterial overgrowth, gum inflammation, and cavities with probiotic supplementation of L. rhamnosus (25, 26).

Genitourinary Infections

Various strains of L. rhamnosus have been shown effective in treating urinary tract infections (UTIs) and vaginal infections when given either orally or intravaginally.

What Are The Health Consequences of Unbalanced Lactobacillus in The Gut?

Given the numerous health benefits of lactobacilli, it's reasonable to expect that disruption to healthy and normal colonization could cause many downstream and unfavorable health effects.

Insufficient levels of beneficial Lactobacillus spp. can result in an elevated risk of infections, increased intestinal barrier permeability and inflammation, and decreased protective immunological factors. Dysbiosis has been linked to chronic digestive disorders, allergies, autoimmunity, and metabolic diseases.

The overgrowth of lactobacilli can also cause detrimental health effects, most often related to digestive symptoms like gas, bloating, abdominal pain and discomfort, indigestion, heartburn, reflux, constipation, and diarrhea. Nutrient malabsorption and symptoms of nutrient deficiencies can occur as well. (27)

What Causes Low Levels of Lactobacillus spp.?

Western dietary patterns, including high saturated and trans fats, high salt, and low fiber intake, have been associated with low levels of lactobacilli. A small study observing the effects of a gluten-free diet also noted reduced Lactobacillus spp. (28)

Acute and chronic stress can drastically affect the gut microbiome's composition, reducing beneficial bacteria levels and allowing pathogenic species to overgrow.

What Causes High Levels of Lactobacillus spp.?

Overgrowth secondary to digestive dysfunction, like low stomach acid, insufficient bile acids, pancreatic insufficiency, and reduced intestinal motility, can result in overgrowth of Lactobacillus spp.  

High serum glucose levels have also been associated with increased Lactobacillus spp.

Specific dietary patterns and supplements can overstimulate the growth of lactobacilli, causing overgrowth. Plant-based diets rich in polyphenols, such as the Mediterranean diet, inulin supplementation, Lactobacillus-containing probiotics, and whey and pea proteins, are associated with increased levels of Lactobacillus spp. (28)


How to Test Lactobacillus spp. Levels

Patient-collected fecal and vaginal samples are most commonly ordered to evaluate Lactobacillus colonies in the gastrointestinal tract and vagina.

Comprehensive Stool Test

Comprehensive stool analyses include an in-depth gut microbiome assessment through fecal specimens. Culture and PCR testing methods will analyze the health and quantity of Lactobacillus spp.

Vaginal Microbiome Analysis

A functional vaginal microbiome analysis is often recommended for patients with recurrent vaginal symptoms and infections to identify the diversity and abundance of the vaginal microbiome. Lactobacillus spp., and its most dominant species, are measured.

Foods That Help Increase Lactobacillus spp. Levels

Certain dietary intake patterns are linked to predictable shifts in Lactobacillus levels. If trying to promote the growth of lactobacilli, foods that are correlated with elevated concentrations include (28):

  • Whey and pea protein
  • Unsaturated fats: avocados, nuts (almonds, hazelnuts, pecans, walnuts), seeds (pumpkin, sesame, flax), fish, oils (olive, peanut, canola, corn, soybean)
  • Fiber: whole fruits and vegetables, nuts and seeds, whole grains, legumes
  • Resistant starch: brown rice, beans, lentils, plantains, green bananas, oats, potatoes
  • Cultured milk and dairy
  • Fermented foods: kimchi, sauerkraut, kefir, kombucha, natto, pickled vegetables
  • Polyphenol-rich foods: fruits, vegetables, seeds, tea, cocoa, wine

The Mediterranean diet has been shown to increase Lactobacillus intestinal colonies specifically. A high intake of monounsaturated and polyunsaturated fats, polyphenols and antioxidants, fiber, low glycemic carbohydrates, and vegetables associated with the diet can explain this. (28)

Supplements that Increase Lactobacillus spp. Levels

Prebiotic and probiotic supplements are often recommended to support Lactobacillus growth. Many probiotics are available, each containing a slightly different combination of Lactobacillus strains. The probiotic choice should be based on lab results and desired treatment/health outcomes.  

Prebiotics are nutrients that fuel probiotic species that are categorized into five main groups:

fructans, galactooligosaccharides, starch and glucose-derived oligosaccharides, other oligosaccharides, and non-carbohydrate oligosaccharides. Prebiotic supplements contain one or several of these to support the growth of lactobacilli and other beneficial microbiome bacteria. Probiotic formulas will often also include prebiotics to improve their efficacy.

How to Make Sure You Are Getting High-Quality Lactobacillus spp. Supplements

Good-quality probiotic supplements are essential for their efficacy. The following characteristics have been identified as important properties for lactobacilli to be effective probiotic organisms:

  • Adherence to epithelial cells
  • Reduce pathogenic adherence to epithelial cells
  • Ability to persist and multiply
  • Production of lactic acid, hydrogen peroxide, and antimicrobial chemicals
  • Resistance of vaginal microbicides
  • Safety: noninvasive, noncarcinogenic, and nonpathogenic
  • Formation of a balanced flora

Probiotic supplements' quality, purity, and strength are essential for efficacy. Choosing a cGMP-compliant, third-party-tested supplement ensures that the manufacturer has followed regulatory and quality requirements to produce a safe, effective, and shelf-stable product. Additionally, selecting a probiotic that has listed bacterial strains on the nutritional label that have been proven effective in clinical trials is important. Because the efficacy of probiotics is strain- and disease-specific, both need to be considered when making recommendations and choosing the correct probiotic supplement. (29, 30)



Our understanding of the human microbiome is rapidly evolving as research continues to uncover the multitude of health benefits provided by the beneficial organisms that coexist within the body. Lactobacillus spp. is a group of beneficial lactic acid-producing bacteria that is comprised of over 200 distinct species. While more research is required, existing evidence supports a wide array of health benefits that healthy levels of lactobacilli provide to the body. Specialty labs can help quantify an individual's levels of lactobacilli in the body, and dietary and supplemental interventions can be implemented as needed to ensure healthy Lactobacillus spp. are growing to support a happy and healthy microbiome.

The information provided is not intended to be a substitute for professional medical advice. Always consult with your doctor or other qualified healthcare provider before taking any dietary supplement or making any changes to your diet or exercise routine.
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