Ingredients"Lactococcus casei" does not correspond to any validly recognized probiotic species in current or historical scientific literature. Lactococcus is a distinct bacterial genus (best known for Lactococcus lactis, a cheese-starter organism) that is genetically and physiologically separate from the probiotic bacterium the name "casei" universally refers to in health contexts. The organism intended — found in fermented dairy foods, dietary supplements, and the human gut; sold commercially as Yakult and Actimel; and the subject of thousands of clinical studies — is Lacticaseibacillus casei (formally reclassified in 2020 from its longstanding name Lactobacillus casei). This article covers Lacticaseibacillus casei in full, using that name throughout while noting where the older name Lactobacillus casei remains in common use on product labels and in the pre-2020 research literature.
Lacticaseibacillus casei is an organism that belongs to the largest genus in the family Lactobacillaceae, a lactic acid bacterium (LAB), that was previously classified as Lactobacillus casei. The genus name of this commercially relevant bacterium changed from Lactobacillus casei to Lacticaseibacillus casei as a result of a 2020 large-scale taxonomic reclassification. The full name Lacticaseibacillus casei has only been in use since 2020; before then, this species was called Lactobacillus casei, and both names may still appear on product labels.
The accepted formal binomial is Lacticaseibacillus casei (Orla-Jensen 1916) Zheng et al. 2020, which itself replaced Lactobacillus casei (Orla-Jensen 1916) Hansen and Lessel 1971 (Approved Lists 1980). The species name casei is Latin for "of cheese," reflecting the organism's original isolation from dairy.
Together with Lactobacillus paracasei and Lactobacillus rhamnosus, L. casei forms what is collectively referred to as the L. casei group. Although the strains of this group are commercially valuable as probiotics, the taxonomic status and nomenclature of the L. casei group have long been contentious because of the difficulties in identifying these three species by using the most frequently used genotypic methodology of 16S rRNA gene sequencing. Members of this group are facultatively heterofermentative, have 45–47 mol% DNA G+C content, and have identical peptidoglycan types (L-Lys-D-Asp).
A seismic shift occurred in the probiotics world when the entire Lactobacillus genus underwent reclassification and renaming. There were several sensible reasons: the genus had become one of the largest among bacteria and consisted of microorganisms from diverse environments with differing phenotypes, causing communication confusion. In addition, new genome sequencing techniques allowed a more reliable classification, and the current taxonomy of Lactobacillus was considered highly irregular.
Huys et al. (2006) reported that more than 28% of commercially available probiotic products were labeled incorrectly at the genus or species level because methods that limit taxonomic resolution were used. It should be stressed that health-promoting properties are not attributed at the species level, but to specific strains.
The organism has been identified as facultatively anaerobic or microaerophilic, acid-tolerant, non-spore-forming. It is a non-sporing, rod-shaped, gram-positive microorganism that can be found within the reproductive and digestive tract of the human body. Since L. casei can survive in a variety of environmental habitats, it has been and continues to be extensively studied by health scientists. It is naturally found in the human gut, oral cavity, and fermented dairy products.
Among the best-documented probiotic strains of L. casei, L. casei DN-114001 (Actimel/DanActive) and L. casei Shirota (Yakult) have been extensively studied and are widely available as functional foods. Lactobacillus casei strain Shirota (LcS) is a well-known probiotic strain that was first isolated in 1930, and in 2013 attained generally recognized as safe (GRAS) status from the USFDA.
Commercially, L. casei is used in fermenting dairy products and in its application as a probiotic. They are used to ferment dairy products, often producing foods with improved flavor and texture, and have also been found to produce many bioactive metabolites which can confer host benefits when consumed. Natural food sources in which L. casei is found or used include yogurt, kefir, fermented milks, and certain ripened cheeses.
L. casei is available as a dietary supplement in various strengths and dosage forms. Some dietary supplements that contain L. casei also contain many other ingredients, including other probiotics. Preparations include fermented milk beverages (most prominently Yakult), drinkable yogurts (e.g., Actimel/DanActive), capsules, tablets, sachets, and powders, as well as incorporated into non-dairy matrices. The recently reclassified Lacticaseibacillus casei-01 (formerly Lactobacillus casei-01) may exert different health effects on the host and has an important role in the development of probiotic dairy and non-dairy foods.
The consumption of fermented foods for their beneficial health effects is an old practice; yogurt, cheese, and other fermented foods were widely consumed in ancient Egypt, China, India, and Africa for their health benefits. Early scientific insights into probiotics followed Louis Pasteur's discovery of the role of microbes in fermentation. In 1907, Élie Metchnikoff, a Russian Nobel Prize-winning scientist, linked improved health and longevity among Bulgarian peasants to the consumption of fermented milk containing Lactobacillus bulgaricus. Although L. casei specifically was not isolated until the twentieth century, the fermented dairy environments in which it naturally flourishes had been in continuous use across human cultures for millennia.
Minoru Shirota (April 23, 1899 – March 10, 1982) was a Japanese microbiologist renowned for his pioneering work in preventive medicine and the development of the probiotic fermented milk drink Yakult. Born in Iida City, Nagano Prefecture, Shirota was deeply influenced by the poverty and widespread diseases he witnessed in early 20th-century Japan, motivating him to pursue a career in medicine. He enrolled at Kyoto Imperial University in 1921, where he studied medicine and earned a Ph.D., later joining the faculty as a lecturer in bacteriology.
He started down the path of microorganism research, focusing on preventive medicine — which places emphasis not on treating illnesses but on trying to prevent them. As part of his research, he discovered that lactic acid bacteria suppress harmful bacteria in the intestines. In 1930, he succeeded in strengthening and culturing a strain of lactic acid bacteria that could survive digestive juices such as gastric fluid and bile, reach the intestines alive, and produce beneficial effects. This strain is now known as Lactobacillus casei strain Shirota.
By the early 1930s, Shirota created a fermented milk drink incorporating the strain, formulated as an affordable daily supplement accessible to everyday people rather than limited to clinical settings. He used the isolated bacterium to treat diarrhoea during an outbreak. Using his bacterium, Shirota prepared a fermented milk which he found was health beneficial for the digestive system. In 1935, he produced the first commercial probiotic beverage, which he named Yakult (meaning yogurt).
The company continued to expand, and in 1955, Yakult Honsha was established. From the 1960s to 1970s, Dr. Minoru Shirota and other Japanese scientists conducted a series of clinical experiments around Yakult and the LcS strain. One study on the effect of Yakult on the incidence of shigellosis in soldiers demonstrated that Yakult products containing LcS have a significant role in preventing specific pathogen infections. In 1935, Yakult probiotic beverages were produced and sold in Japan. In 1964, Yakult's first overseas branch was established in Taiwan. Since then, it has sold Yakult in more than 32 countries and regions around the world, including Brazil, Thailand, South Korea, Mexico, Australia, the United Kingdom, Germany, and mainland China.
The concept of "preventive medicine" and the idea that "a healthy intestinal tract leads to a long life" are foundational to the philosophy that drove Shirota's original research. Dr. Shirota's research with the L. casei Shirota strain, which started in 1930, was taken over by the Yakult Central Institute in 1955. With a total listing of over 500 scientific studies (both in Japanese and in English), it is fair to say that the L. casei strain Shirota is among the most researched probiotic strains in the world.
Between the 1970s and 1990s, the use of probiotics for gut health increased in Asia and Europe. The L. casei group became central to the burgeoning fermented foods industries in both regions, with L. casei-containing yogurts and dairy beverages becoming mainstream consumer health products from the late twentieth century onward. The widely known probiotic strains of this group, such as L. casei strain Shirota and L. rhamnosus GG, are used worldwide in fermented dairy products or food supplements and as probiotics to enhance host health.
L. casei makes a substance called lactic acid. This is its primary and most quantitatively significant metabolic output during fermentation. Lactic acid is a short-chain organic acid that lowers the pH of the local environment, creating conditions hostile to many pathogenic microorganisms. The inhibition produced by lactic acid bacteria may be due to the production of organic acids such as lactic, propionic and acetic, hydrogen peroxide, bacteriocins, bacteriocin-like substances and possibly biosurfactants, which are active against certain pathogens and may be produced by different species of Lactobacillus.
The production of several substances with microbicidal action — such as acetic acid, bacteriocins, biosurfactants, hydrocarbons, hydrogen peroxide, coaggregation molecules, and lactic acid — have been reported. Among them, lactic acid is considered the most important postbiotic substance.
Potential mechanisms include the production of antimicrobial substances such as bacteriocins, enhancing the epithelial barrier through attachment, competition for pathogenic binding sites, or modulation of the immune system. Bacteriocins are ribosomally synthesized peptides produced by bacteria that exhibit antimicrobial activity against closely related or other bacterial species. Their production by L. casei strains contributes to competitive exclusion of pathogens.
The cell wall architecture and surface-associated molecules of L. casei play important functional roles. Isolated L. casei strains harbor one or even two large, glycosylated putative surface adhesins. This might inspire further exploration of this species as a potential probiotic organism. These surface adhesins are thought to enable firm attachment to intestinal epithelial cells, a prerequisite for effective colonization and host interaction.
Members of the L. casei group are facultatively heterofermentative, have 45–47 mol% DNA G+C content, and have identical peptidoglycan types (L-Lys-D-Asp). The peptidoglycan of L. casei is recognized by innate immune pattern-recognition receptors in the host, contributing to immunomodulatory signaling.
In recent years, paraprobiotic and postbiotic forms derived from probiotic strains have gained attention. The recently reclassified Lacticaseibacillus casei-01 may exert different health effects on the host both as a live organism and via bioactive compounds released during or after its activity. Postbiotics from L. casei — including cell wall fragments, metabolic byproducts, and secreted proteins — have been shown in ex-vivo research to retain immunomodulatory and anti-inflammatory activity even in the absence of live bacterial cells.
It is commonly believed that these bacteria stabilize gut microflora, inhibit the development of pathogenic microorganisms, eliminate or minimize symptoms of lactose intolerance, prevent or alleviate the course of bacterial, viral and post-antibiotic diarrheas, as well as normalize disorders of gut peristalsis. Competitive exclusion operates through multiple mechanisms simultaneously: physical occupation of epithelial binding sites, production of organic acids that lower luminal pH, and secretion of bacteriocins.
Probiotics can act to modulate the existing intestinal microbiota, produce mediators that can modify the inflammatory response and gastrointestinal function, improve intestinal barrier function, and alter the host immune response. Strengthening of tight junctions between enterocytes reduces translocation of luminal antigens and pathogens into systemic circulation, contributing to the anti-inflammatory profile associated with L. casei.
Lactic acid bacteria are claimed to have immunomodulating effects. Stimulation as well as suppression of T-helper (Th)1-mediated immune responses have been described for various strains. Experiments involving Lactobacillus casei Shirota (LcS) detected mainly enhancement of innate immune responses and promotion of Th1-mediated immune reactivity.
Rather than overstimulating immunity, strains like L. casei Shirota activate essential immune cells such as CD8⁺ T cells and natural killer cells, while also encouraging the release of both pro-inflammatory and anti-inflammatory cytokines. This ensures the immune system is alert but not overreactive.
At baseline in post-infectious IBS patients, IL-1α, IL-6 and IL-8 mRNA levels as well as TLR-4 protein expression were significantly higher, while IL-10 mRNA levels were lower, compared to healthy controls in both ileum and colon. L. casei DG and its postbiotic significantly reduced the mRNA levels of pro-inflammatory cytokines and TLR-4 while increasing that of IL-10 after LPS stimulation. The protective effect was more pronounced for the postbiotic than live bacterial treatment.
Introduction of probiotics to the intestines can modulate gut microbiota composition and in turn regulate the host immune system and modify the inflammatory response. Probiotics can also improve intestinal barrier function and exhibit a positive impact on host physiological and pathological conditions via gut microbiota-derived metabolites.
Research has identified gut metabolites as mediators of specific beneficial effects of L. casei. In a constipation study, LcS intervention significantly improved defecation frequency (from 4.81 to 7.81 times per week, p < 0.05), stool consistency (from 2.52 to 3.68, p < 0.05), and constipation-related symptoms. A total of 14 non-volatile fecal metabolites were obtained as potential constipation-related metabolites that were regulated by LcS.
L. casei is a widely used food-grade probiotic bacterium with strain-specific evidence for reducing antibiotic-associated diarrhea, improving some IBS symptoms, and modulating mucosal immunity.
Antibiotic-Associated Diarrhea (AAD): The gut microbiome is dramatically altered early in antibiotic use and during ICU stays, increasing the risk for antibiotic-associated diarrhea (AAD) and Clostridium difficile infections (CDI). Evidence suggests that some probiotics are effective in the primary prevention of AAD and CDI. A feasibility clinical trial examined L. casei for this indication: ICU patients initiated on antibiotics were recruited and matched with contemporary controls. Study patients received two bottles daily of a drink containing 10 billion Lactobacillus casei bolused via feeding tube. Tolerance to probiotics and enteral nutrition, development of adverse events, and incidence of AAD were recorded. CDI rates were followed for 30 days post-antibiotic treatment. Thirty-two patients participated in the trial. There were no serious adverse events in the probiotic group, compared to three in the control group. This was a small feasibility study; the evidence for AAD prevention by L. casei is promising but requires confirmation in larger, adequately powered trials.
Historical evidence for pathogen inhibition: Lactobacillus casei strain Shirota was employed to battle diarrheal outbreaks. A probiotic product with this strain was among the early predecessors in a scientific field that has since blossomed.
A pivotal randomized controlled trial assessed the effect of LcS on IBS symptoms: Meta-analyses point to a modest but significant effect of probiotics on symptoms in IBS. This RCT aimed to assess the effect of Lactobacillus casei Shirota (LcS) on symptoms and quality of life in IBS patients. IBS patients (Rome II criteria) between 18 and 65 years of age were included. The study consisted of an 8-week intervention period in which participants received probiotic (LcS) or placebo twice daily, followed by an 8-week follow-up period. Symptom diaries and quality of life were scored at weeks 0, 8 and 16. The primary outcome was a decrease of at least 30% in a composite mean symptom score (MSS) at week 8. Thirty-nine individuals (67% women) were included in the probiotic group and 41 individuals (71% women) were included in the placebo group.
The combined use of L. casei strains in IBS has also been studied: a double-blind, randomised, placebo-controlled study examined Lactobacillus acidophilus CL1285, Lactobacillus casei LBC80R and Lactobacillus rhamnosus CLR2 for improving quality-of-life and IBS symptoms, published in Beneficial Microbes, vol. 9.
An ex-vivo organ culture model specifically investigated Lactobacillus casei DG (LC-DG) in post-infectious IBS (PI-IBS). The aim was to evaluate the role of Lactobacillus casei DG and its postbiotic in modulating the inflammatory/immune response in PI-IBS. Ex vivo cultures of ileal and colonic mucosa from 10 PI-IBS diarrhea-predominant patients, and 10 healthy controls, were treated with LPS, LC-DG, and its postbiotic. While this ex-vivo model provides mechanistic insights, clinical translation requires further confirmation in powered human trials.
Overall, the evidence for L. casei in IBS is preliminary to moderate. Lactobacillus spp. positively affect IBS symptoms, although the mechanisms through which probiotics exert their beneficial effects are largely unknown.
A human clinical study investigated the effect of L. casei Shirota (LcS) on constipated patients. The study investigated the effects of LcS on constipated patients and revealed that a metabolite mediator is involved in the LcS-induced constipation alleviation. Sixteen constipated patients and 22 non-constipated participants were recruited. The subjects consumed 100 mL of an LcS beverage (10⁸ CFU/mL) per day for 28 days. In constipated patients, LcS intervention significantly improved defecation frequency (from 4.81 to 7.81 times per week, p < 0.05), stool consistency (from 2.52 to 3.68, p < 0.05), and constipation-related symptoms. A total of 14 non-volatile fecal metabolites were identified as potential constipation-related metabolites regulated by LcS. This was a small study; its metabolite findings are mechanistically interesting but preliminary.
Numerous experiments have indicated that changes in the intestinal microbiota can cause immunomodulation, both at the intestinal and the systemic level. Especially lactic acid bacteria, which are part of the human commensal microbiota and have a long history of use in food products, have been widely studied. The ability of several LAB strains to modulate host innate as well as acquired immune responses has been demonstrated in many in vitro experiments and animal models.
In animal models, L. casei has shown protective effects against respiratory infections like influenza and has also helped reduce allergic skin reactions by promoting regulatory T cells and calming inflammation without suppressing the immune response. These are animal findings; human translation requires further clinical research.
A systematic evaluation and analysis of 33 clinical studies found that probiotics were effective in 21 studies, with strains from Bifidobacterium and Lactobacillus being regarded as the most effective choices, with the clinical remission rate significantly higher than that of placebo groups. Lactobacillus, as an important representative of probiotics (including Lactobacillus casei), has functional characteristics that exceed the traditional understanding of acid-producing and antibacterial effects. The latest research shows that Lactobacillus has multiple physiological functions, such as regulating the intestinal microecology, protecting the digestive system, and regulating the immune system.
Previous studies have demonstrated that Lactobacillus casei strain Shirota (LcS) treatment could inhibit clinical manifestation of colitis in dextran sulfate sodium (DSS)-induced mice; however, the underlying mechanisms remained unknown at the time of these animal studies. Animal model findings require careful extrapolation to human IBD contexts.
A laboratory study assessed the inhibitory effects of L. casei Shirota against Candida species: L. casei Shirota showed inhibitory action against all tested Candida spp., ranging from 66.9 to 95.6% inhibition depending on the species. This inhibition is possibly related to the production of lactic acid, since lactic acid has shown microbicidal action against these same Candida spp. at a concentration of 5 mg/mL, which corresponds to half of the normal physiological concentration. These are in vitro findings; clinical studies in humans on the use of L. casei specifically for vaginal candidiasis are limited.
In co-culture, Lactobacillus casei Shirota inhibits the growth of E. coli UAM0403, while the growth of Lactobacillus casei Shirota was not influenced by the presence of this harmful bacterium. The ability of lactic acid bacteria to inhibit the growth of pathogenic bacteria is well-known. Lactobacilli are able to compete with pathogenic bacteria when incubated together, but the degree of inhibition is bacterial strain-dependent. These in vitro findings are supportive of clinical observations but should not be directly extrapolated to in vivo outcomes without human study confirmation.
Studies suggest that lactic acid bacteria play an important role in the host's immunoprotective system by increasing specific and non-specific mechanisms to have an anti-tumour effect. Lactobacillus casei Shirota (LcS) has been shown to have potent anti-tumour and anti-metastatic effects on transplantable tumour cells and to suppress chemically induced carcinogenesis in rodents. Research by Hideki Ishikawa of the Kyoto Prefectural University of Medicine demonstrated that Lactobacillus casei powder can be used for prevention of colorectal tumors; details were published in Nature Clinical Practice Gastroenterology & Hepatology in 2005. This human study is notable, but the overall evidence base for L. casei in cancer prevention remains preliminary and requires large-scale confirmatory trials.
Many studies have shown that strains belonging to the L. casei group may decrease lactose intolerance, the effects of inflammatory bowel disease, diarrhea, constipation, food allergies, and even colon cancer. Moreover, evidence exists of positive effects of these bacteria on mucosal immunity and blood cholesterol level. These effects are largely based on observational data, in vitro studies, and small clinical trials; the quality of evidence for cholesterol reduction specifically remains limited and heterogeneous.
While many of these strains have been shown to have an effect in in vitro or in vivo mouse models, the underlying mechanisms require further research for any future use as microbial therapeutics.
Health benefits associated with the L. casei group have been reported for a variety of health conditions, ranging from atopic dermatitis to cancer. The following body systems and health areas have been the subjects of research:
Much research has focused in recent years on the application of the L. casei group for health promotion in treatment or prevention of a number of diseases and disorders. The LCG have the potential to be used prophylactically or therapeutically in diseases associated with a disturbance to the gut microbiota.
Dosages used in L. casei research are strain- and preparation-specific and are expressed in colony-forming units (CFU). The following dosages are drawn directly from cited studies:
The health benefits associated with consumption of live and inactivated L. casei-01 cells, the factors influencing its survival in food products, and the impact of its addition on the quality parameters of dairy and non-dairy products are all considerations relevant to dosage form selection. Viability to the gut is a key practical concern; enteric-coated or microencapsulated preparations are designed to protect the live organisms through the acidic gastric environment.
In immunocompetent adults, L. casei is generally safe; common adverse events are mild gastrointestinal symptoms — bloating (approximately 5–20%) and transient flatulence. Rare invasive infections (bacteremia/endocarditis) occur in fewer than 0.01% of the general population, but rates are higher in severely immunocompromised or catheterized patients.
Although probiotics are generally considered safe, their safety in immunocompromised patients is uncertain. Lactobacillus species, being a normal body flora, have generally not posed much concern about causing disease in immunocompetent individuals. In fact, they are considered contaminants or opportunistic pathogens when isolated from specimens belonging to immunocompetent individuals. Increasing reports on Lactobacillus bacteremia-associated morbidity and mortality in immunocompromised patients have raised concerns about the safety of probiotic use in this group.
A documented case report illustrates this risk: A rare case of Lactobacillus casei endocarditis was reported in a 71-year-old female, immunocompromised due to chronic steroid intake, who presented with a productive cough and low-grade fever. Blood cultures grew L. casei resistant to vancomycin and meropenem. Transesophageal echocardiography showed mitral and aortic vegetations; valve replacement was performed after successfully removing vegetations. She was treated with a six-week course of daptomycin and recovered.
A few recent cases of bacteremia and/or sepsis associated with lactobacilli have been reported in patients with different underlying diseases such as ulcerative colitis in pediatric or adult patients, suggesting that extensive damage of the colonic mucous membrane increases the risk of bacteremia. Other cases involve HIV-infected populations or other immunocompromised patients. Three cases of L. casei sepsis were described in a pediatric intensive care unit, two of which with congenital heart disease and the third one with a cervical spinal cord injury.
In very rare cases, particularly among people with weakened immune systems such as those undergoing chemotherapy or recovering from major surgery, L. casei has been linked to infections like bacteremia or heart valve inflammation. Though these cases are extremely uncommon, they highlight the need for caution in high-risk groups.
Antibiotic resistance is a point worth considering. Studies show that while most L. casei strains are safe and do not carry transferable resistance genes, a few have shown mild resistance to certain antibiotics. This is why proper strain screening and quality control are essential in probiotic manufacturing.
Antibiotics can inactivate bacterial probiotics; separation of doses by 2–3 hours is recommended to improve co-administration effectiveness. Relevant antibiotics include amoxicillin, clindamycin, ciprofloxacin, and azithromycin. The recommendation is to space dosing by 2–3 hours and continue the probiotic 1–4 weeks after antibiotic completion.
Medications such as tacrolimus, mycophenolate, systemic corticosteroids, and TNF inhibitors carry an interaction type of increased risk of opportunistic infection from live organisms. Live probiotic organisms should be used with caution in patients on these agents.
Lactobacillus casei strain Shirota attained generally recognized as safe (GRAS) status from the USFDA in 2013. The FDA has not reviewed L. casei as a whole for safety and effectiveness as a drug. It is marketed and regulated as a dietary supplement and/or food ingredient in most jurisdictions.
The taxonomic status of the L. casei group has long been contentious; methods with inadequate taxonomic resolution have been used, leading to species being mislabeled in products, publications, and some publicly available DNA sequences. Consumers and clinicians should be aware that strain identity on product labels may not always reflect genomic classification accurately.
Health conditions that Lactococcus casei may help support.
Body systems that Lactococcus casei may help support.
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