Lactobacillus gasseri
1. Identity, Taxonomy, and Classification
Scientific Nomenclature and Taxonomy
Lactobacillus gasseri is a gram-positive, non-motile, non-spore-forming, rod-shaped bacterium belonging to the order Lactobacillales, family Lactobacillaceae. Initially, L. gasseri was indistinguishable from L. acidophilus by phenotypic and metabolic analysis and was not classified as a separate organism until after distinct subgroups were observed in the electrophoretic characterization of lactate dehydrogenases from L. acidophilus (Gasser, 1970; Gasser et al., 1970). Lactobacillus gasseri was ultimately defined as a separate organism based on DNA-DNA hybridization techniques (Lauer & Kandler, 1980; Lauer et al., 1980).
In April 2020, a polyphasic taxonomic review published in the International Journal of Systematic and Evolutionary Microbiology (IJSEM) proposed the reclassification of the genus Lactobacillus into 25 genera, including the creation of 23 novel genera such as Ligilactobacillus. Under this formal reclassification, L. gasseri was reassigned to the genus Ligilactobacillus, making its currently valid taxonomic name Ligilactobacillus gasseri. However, species names and strain designations have not changed, and the name Lactobacillus gasseri remains in wide use across the scientific and regulatory literature.
The plasmid-free genome of the neotype strain ATCC 33323 was 1,894,360 bp in size and predicted to encode 1,810 genes. The GC content was 35.3%, similar to its closest relatives, L. johnsonii NCC 533 (34%) and L. acidophilus NCFM (34%). The bacterium is an obligate saccharoclastic, homofermentative organism, with an optimum growth at 35 to 38°C, and forms small rods with rounded ends from 0.6 to 0.8 by 3 to 5 μm in size.
Taxonomic Note: Lactobacillus paragasseri
Three strains previously classified as Lactobacillus gasseri were investigated using a polyphasic taxonomic approach. Although these strains shared high 16S rRNA gene sequence similarities with L. gasseri ATCC 33323T (99.9%), they formed a clade clearly distinct from ATCC 33323T based on whole-genome relatedness; average nucleotide identity and in silico DNA–DNA hybridization values fell below the thresholds used to distinguish species. Based on these analyses, these strains were formally proposed as a novel species, Lactobacillus paragasseri sp. nov. It is important to note that studies associating L. gasseri in the urogenital microbiota and symptom status predate the discovery of L. paragasseri, meaning some findings attributed to L. gasseri in the older literature may relate to what is now classified as L. paragasseri.
Natural Sources and Ecological Niches
Lactobacillus gasseri ATCC 33323, previously known as "F. Gasser 63 AM," is a strain of human origin and a normal inhabitant of the mouths, intestines, feces, and vaginas of juveniles and adults. It is an autochthonous microorganism that colonizes the human mucosa, including the oral cavity, vagina, and gastrointestinal tract in healthy individuals, and is among the predominant microorganisms in the initial colonization of the neonatal GIT following childbirth.
Many of today's probiotic strains, including L. gasseri and L. reuteri, were isolated from the human stomach. Lactobacillus gasseri BNR17 is a type of probiotic strain isolated from human breast milk. L. gasseri was originally isolated from the human gut, but it also shows up in fermented milk products where lactic acid bacteria thrive.
In terms of food sources, Lactobacillus gasseri is found naturally in a small number of fermented foods, most notably certain fermented dairy products like yogurt, kefir, and some traditionally fermented vegetables. Certain yogurts are made with L. gasseri as a starter culture, particularly in Japan, where the strain SBT2055 has been commercially added to yogurt for years. Kefir, a tangy fermented milk drink, contains a diverse mix of bacterial and yeast species, and L. gasseri has been identified among the many strains present in traditional kefir grains, though the exact bacterial profile varies depending on the origin of the grains and fermentation conditions.
Some traditionally fermented vegetables harbor L. gasseri, though less reliably than dairy. Naturally fermented pickles (the kind made with salt brine, not vinegar), sauerkraut, and kimchi all create environments where various lactobacillus species can flourish, and L. gasseri has been detected in some of these foods, but it is not a dominant species in most batches.
Common Supplemental Strains and Forms
Several well-characterized strains are the focus of the majority of clinical research:
- SBT2055 (LG2055) — Commercially incorporated into fermented milk products in Japan; the most extensively studied strain for metabolic and weight outcomes.
- BNR17 — Isolated from human breast milk; previously demonstrated to inhibit obesity- and diabetic-related activities in animal models before being progressed to human clinical trials.
- OLL2716 (LG21) — Primarily studied in relation to Helicobacter pylori suppression and upper GI function.
- OLL2809 — Studied in relation to endometriosis-associated dysmenorrhea.
- ATCC 33323 — The internationally recognized neotype, or reference strain, used in fundamental genomic and mechanistic research.
L. gasseri is available as a dietary supplement in various strengths and dosage forms. Commercial preparations include capsules, powders, fermented milk products, and probiotic-containing yogurts. In the United States, prior sanctions from the FDA permit the use of harmless lactic acid-producing bacteria, including L. gasseri species, as optional ingredients in certain specified standardized foods, including cultured milk (21 CFR 131.112), sour cream (21 CFR 131.160), cottage cheese (21 CFR 133.128), and yogurt (21 CFR 131.200).
2. Traditional and Historical Context
Although Lactobacillus gasseri was only isolated and identified as a distinct species in the 1980s, the benefits associated with it have been unknowingly utilized through traditional fermented foods and dietary practices for centuries. Lactic acid bacteria have been used since ancient times in the preservation and production of traditional fermented foods.
The broader acidophilus complex, of which L. gasseri is a part, was first described by Moro (1900) as Bacillus acidophilus, and was renewed by Hansen and Moquot (1970). Together with other species relevant for probiotics, L. gasseri as a distinct organism was described in the years 1980 to 1992. L. gasseri was originally identified as Lactobacillus acidophilus based on indistinguishable phenotypic and metabolic characteristics prior to formal reclassification.
Because L. gasseri is a naturally occurring component of the human gut microbiota and a commensal inhabitant of fermented dairy environments, it was not recognized as a discrete microorganism during the historical periods when fermented foods were first being consumed. Like other lactic acid bacteria, L. gasseri is found in fermented dairy products such as yogurt and kefir, as well as in fermented vegetables. While early societies were unaware of its microbial identity, they understood that consuming these foods enhanced digestion, protected against illness, and promoted vitality. There is no documented tradition of using an identified L. gasseri preparation for specific medicinal purposes in any historical pharmacopeial or herbal tradition, as its identity as a distinct species was established only in modern microbiology. Its "traditional use" is therefore best understood as an incidental component of the broader fermented food heritage common to cultures worldwide.
In Japan specifically, the strain SBT2055 has been commercially added to yogurt for years, representing one of the earliest deliberate consumer applications of a named L. gasseri strain.
3. Key Constituents, Active Compounds, and Mechanisms of Action
Lactobacillus gasseri is a living microbial organism rather than a plant extract with isolable chemical constituents. Its biological activity is understood through a set of molecular and physiological mechanisms documented in peer-reviewed research.
3.1 Lactic Acid and Acidification
Lactic acid bacteria are defined by organisms whose primary metabolic product from the fermentation of sugars is lactic acid. This acidification of local environments — in the gut, vagina, or gastric mucosa — lowers pH, which directly inhibits the growth of acid-sensitive pathogens. When H. pylori strains were co-cultivated with L. gasseri OLL2716, the bacteria converted from rod to coccoid form within 24 hours, a dormant, non-replicating state attributed in part to local lactic acid production.
3.2 Bacteriocin Production
L. gasseri exerts its beneficial effects through biological processes that modify the local environment and interact directly with the host. One mechanism is the production of specialized antimicrobial peptides known as bacteriocins, such as gassericin A. These molecules actively inhibit the growth of various harmful microorganisms, including Gram-positive and Gram-negative pathogens.
Gassericin A is a circular bacteriocin. Bacteriocins are ribosomally synthesized and often undergo post-translational processing such as hydrolysis of leader peptides. In class II bacteriocins, hydrolysis occurs at a conserved gly-gly motif that is absent in circular bacteriocins, which are predicted to have a different processing site. Secretion is achieved using a dedicated ABC transporter and circularization occurs enzymatically.
Gassericin A, produced by L. gasseri LA39, was determined to be one of the most widely active bacteriocins of the acidophilus group and was bactericidal without causing cell lysis.
Bioinformatics analysis of L. gasseri strains has revealed that the species harbors operons for four distinct classes of bacteriocins: class IIb (gassericin T), class IIc (acidocin B), class IId (bacteriocin LSchainb), and class III (helveticin J). L. gasseri LA327, isolated from the large intestine tissue in humans, is a bacteriocinogenic strain with two kinds of class IIb bacteriocin structural genes, i.e., those for gassericin T (GT) and acidocin LF221A.
3.3 Hydrogen Peroxide Production
Lactobacilli are able to inhibit pathogens in a direct manner by coaggregation or by producing active components such as bacteriocins, lactic acid, and hydrogen peroxide (H₂O₂). The production of H₂O₂ is particularly relevant to the vaginal environment, where it contributes to the suppression of anaerobic pathogens associated with bacterial vaginosis.
3.4 Epithelial Adhesion and Competitive Exclusion
Lactobacillus gasseri is an autochthonous microorganism which has been evaluated for probiotic activity based on the availability of genome sequence and species-specific adaptation to the human mucosa. Niche-related characteristics contributing to indigenous colonization include tolerance of low pH environments, resistance to bile salts, and adhesion to the host epithelium.
The bacterium also adheres strongly to the epithelial lining of the intestine and other mucosal surfaces. This ability allows it to physically block adhesion sites, a process known as competitive exclusion, preventing pathogenic bacteria from colonizing the host tissue.
In genome sequence analysis, L. gasseri was found to encode the highest number of putative mucus-binding proteins (14) among lactobacilli sequenced to date, a feature consistent with its strong mucosal colonization capacity.
3.5 Intestinal Barrier Integrity
In addition to direct pathogen inhibition, lactobacilli promote the integrity of the epithelium by stimulating mucus secretion and modulating the immune response, which are indirect ways of inhibiting viral and bacterial pathogens. Research in animal models has provided additional mechanistic detail: experimental findings in a DSS-induced colitis mouse model revealed that L. gasseri ATCC33323 significantly improved physiological damage, reduced the severity of colonic inflammation, decreased inflammatory factors, and preserved the integrity of the intestinal epithelial structure and function, while also maintaining the expression and localization of adhesive proteins and improving intestinal barrier permeability.
3.6 Immunomodulation
In humans, L. gasseri elicits various health benefits through its antimicrobial activity, bacteriocin production, and immunomodulation of the innate and adaptive systems. Specifically, L. gasseri exhibits bile resistance, adhesion to Caco-2 intestinal epithelial cells, antimicrobial activity, the ability to degrade oxalate, and immunomodulatory properties.
3.7 Exopolysaccharide (EPS) Production
Analysis of the L. gasseri genome revealed a putative exopolysaccharide (EPS) gene cassette. EPSs are carbohydrate polymers that can be secreted into the environment or remain attached to the cell wall, and these polymers have been shown to influence the adhesion properties of probiotic and pathogenic strains.
3.8 Carbohydrate Metabolism and Mucin Utilization
Among the fermentable carbohydrates of L. gasseri, N-acetyl-d-galactosamine, d-galactose, sialic acid, and l-fucose are components of the oligosaccharide side chains of epithelial mucin glycoproteins. Thus, secreted mucin glycoproteins that pass through or are present in the GIT represent an important nutrient source for this resident microflora, supporting stable colonization of the intestinal mucus layer.
4. Scientific Evidence by Health Area
4.1 Metabolic Health: Body Weight and Abdominal Adiposity
This is the most extensively studied clinical area for L. gasseri as a dietary supplement.
Strain SBT2055 (LG2055): Kadooka et al. reported that supplementation of fermented milk with Lactobacillus gasseri SBT2055 for 12 weeks induced significant weight loss and a decrease in abdominal visceral and subcutaneous fat mass in overweight adults under ad libitum conditions. The results showed a significant reduction in abdominal visceral and subcutaneous fat areas (4.6% and 3.3%, respectively, P < 0.01), body weight (1.4%, P < 0.001), BMI (1.5%), and waist (1.8%) and hip (1.5%) circumferences for the intervention group compared with baseline.
Strain BNR17: A clinical study investigated the effect of BNR17, a probiotic strain isolated from human breast milk, on obese and overweight adults. Sixty-two obese volunteers aged 19 to 60 with a body mass index ≥ 23 kg/m² and fasting blood sugar ≥ 100 mg/dL participated in a placebo-controlled, randomized, double-blind trial. For 12 weeks, 57 participants were given either placebo or BNR17 and were assessed by measuring body fat, body weight, various biochemical parameters, vital signs, and computed tomography. Visceral adipose tissue (VAT) was significantly decreased in the high-dose BNR17 group compared with the placebo group (P = .038), with a mean difference of −21.6 cm² at 12 weeks (P = .012). Waist circumferences were significantly decreased in both the low- and high-dose BNR17 groups compared with baseline values, but not in the placebo group.
Evidence Assessment: The efficacy of L. gasseri on weight loss is strain-sensitive. Two well-known strains, BNR17 and SBT2055, have been used in many animal and clinical studies, with more evidence available for SBT2055 than BNR17. Clinical studies have documented significant reductions in visceral adipose tissue ranging from 4.6% to 8.5% in placebo-controlled trials. Although several randomized controlled trials have explored the ability of Lactobacillus to improve metabolic parameters in adults who are overweight or obese, their findings have been inconsistent and require further analysis. Effects are modest and were observed primarily in individuals with elevated BMI; the trials to date have been relatively small and short (predominantly 12 weeks), and industry funding is a documented limitation of some published studies.
4.2 Gastric Health: Helicobacter pylori Infection
Helicobacter pylori is a common gastric pathogen with infection resulting in acute mucosal damage and the possible clinical manifestation of peptic ulcers, gastritis, and gastric cancer due to chronic infection. Current treatments include administration of antibiotics, which often result in the alleviation of symptoms, but not necessarily eradication of H. pylori.
To examine the efficacy of Lactobacillus gasseri OLL2716 (LG21) as a probiotic for Helicobacter pylori in humans, 31 subjects infected with the bacterium ingested yogurt containing LG21 daily for an 8-week period. The [¹³C]urea breath test and assays of serum pepsinogens revealed a significant improvement following LG21 treatment. LG21 was thus determined to be effective in both suppressing H. pylori and reducing gastric mucosal inflammation.
A larger multicenter randomized double-blind controlled trial examined LG21 in the context of dyspeptic symptoms: 131 participants who met the selection criteria (mean age 48.9 years) were randomly given L. gasseri OLL2716-containing yogurt or placebo yogurt once daily for 12 weeks. No significant differences were observed between the groups in urea breath test results, H. pylori stool antigens, or the serum PGI/II ratio; however, in the L. gasseri group, postprandial fullness was significantly lower at the end of the trial compared to the initial level (p < 0.05) and significantly fewer patients had a VAS score of >10 for bloating compared to the placebo group (p < 0.05).
Additionally, a pretreatment protocol was studied: A total of 229 patients were randomized either to 1 week of triple therapy (rabeprazole, amoxicillin, and clarithromycin) or triple therapy plus L. gasseri-containing yogurt. In the yogurt-plus-triple therapy group, yogurt containing L. gasseri OLL2716 (112 g) was consumed twice daily for 4 weeks (3 weeks pretreatment followed by 1 week during eradication therapy).
The LG21 strain has been detected in the gastric mucus layer and, although it does not permanently colonize the stomach, it is believed to temporarily attach; with continuous intake, it can be expected to act in the upper digestive tract. Clinical studies have confirmed that the activity of H. pylori in the stomach is suppressed by continuous ingestion of the LG21 strain.
Evidence Assessment: The evidence for strain OLL2716 in suppressing H. pylori activity and alleviating associated dyspeptic symptoms is supported by multiple clinical trials of moderate size. However, complete eradication of H. pylori using L. gasseri alone has not been demonstrated; the strain appears to exert a suppressive rather than eradicative effect. Adjuvant use alongside standard triple therapy warrants further confirmatory trials.
4.3 Vaginal Health and Bacterial Vaginosis
In humans, L. gasseri elicits health benefits through its antimicrobial activity, bacteriocin production, and immunomodulation of the innate and adaptive systems. The clinical trial evidence supporting use of L. gasseri in probiotic applications includes maintenance of vaginal homeostasis and amelioration of diarrhea.
A randomized controlled clinical trial investigated oral administration of L. gasseri TM13 and L. crispatus LG55 in bacterial vaginosis (BV): Women attending a gynecology outpatient clinic who presented with abnormal leucorrhoea symptoms were enrolled in a single-center, prospective, parallel-group, randomized controlled clinical trial. Inclusion criteria were age 18–55 years, premenopause, with a history of sexual activity, and a Nugent Score ≥ 7. The strains showed a strong ability to lower vaginal pH and inhibit the growth of pathogenic bacteria and fungi, and alleviated the inflammatory response of BV rats in preclinical testing.
Bacterial vaginosis is a microecological disorder caused by decreased abundance of lactobacilli and an increased abundance of anaerobic bacteria, commonly affecting the female lower genital tract. The prevalence of BV is around 20–30% worldwide, and it increases the susceptibility of women of reproductive age to sexually transmitted infections including HIV, HPV, and gonorrhea, and increases the risk of spontaneous abortion, preterm delivery, and amniotic fluid infection during pregnancy.
Evidence Assessment: The clinical evidence for L. gasseri in maintaining vaginal health and supporting BV recovery is biologically plausible and supported by genomic, preclinical, and emerging clinical data. However, the available clinical trials are limited in number and sample size. The relationship between oral L. gasseri administration and vaginal microbiota restoration remains an active area of investigation with preliminary but not yet definitive human evidence.
4.4 Dysmenorrhea and Endometriosis
A randomized, double-blind, placebo-controlled study examined L. gasseri OLL2809 in patients with endometriosis-associated pain: Lactobacillus gasseri OLL2809 was evaluated for its effects on menstrual pain and dysmenorrhea in endometriosis patients in a randomized, double-blind, placebo-controlled study (2011). L. gasseri improved menstrual pain and dysmenorrhea in patients with endometriosis in this trial. Preclinical research has also shown activity: L. gasseri inhibited the growth of endometrial tissue in the abdominal cavity in mice and rats.
Evidence Assessment: The human clinical evidence for L. gasseri in endometriosis is very limited and derives predominantly from a single strain (OLL2809) in a single published randomized trial. While the result was statistically significant and supported by animal model data, independent replication in larger trials is needed before clinical conclusions can be drawn. This area should be characterized as preliminary.
4.5 Gastric Motility and Functional Dyspepsia
A double-blind, parallel-group, placebo-controlled randomized trial assessed L. gasseri OLL2716 on gastric emptying: The effects of L. gasseri OLL2716 (LG21 strain) on mild to moderate delayed gastric emptying were evaluated in a randomized trial. Participants (n = 28) were randomly assigned to ingest LG21 strain-containing yogurt or LG21 strain-free yogurt for 12 weeks. The ¹³C gastric emptying breath test was performed to measure the gastric emptying rate, and the time to reach the peak (Tmax) was used as an indicator.
Evidence Assessment: The sample size in this trial (n = 28, with per-protocol analysis of n = 27) is small. The finding is hypothesis-generating and requires replication in larger, more adequately powered trials.
4.6 Diarrhea and Gastrointestinal Infections
The genomic and empirical evidence supporting use of L. gasseri in probiotic applications is substantiated by clinical trial data including amelioration of diarrhea. Preclinical work has further demonstrated pathogen-suppressive effects: in a mouse model using C57BL/6J mice given gavage doses of 10⁹ CFU/day of different bacteriocin-producing L. gasseri strains, the ability of different L. gasseri strains to alleviate symptoms caused by Salmonella typhimurium infection was investigated. However, large-scale human randomized controlled trials specifically addressing L. gasseri for infectious or antibiotic-associated diarrhea remain sparse in the literature, and this area is primarily supported by genomic plausibility and smaller studies.
4.7 Colitis and Inflammatory Bowel Conditions
In a DSS-induced colitis mouse model, Lactobacillus gasseri ATCC33323 was selected from the intestinal microbiota to investigate its mechanisms in colitis. The strain significantly improved physiological damage in colitic mice, reduced the severity of colonic inflammation, decreased the production of inflammatory factors, and preserved the integrity of the intestinal epithelial structure and function. Transcriptional analysis and in vitro experiments revealed that L. gasseri ATCC33323 regulates CDH1 transcription by affecting NR1I3, thereby promoting E-cadherin expression; these findings contribute to a better understanding of specific mechanisms by which Lactobacillus strains alleviate colitis, offering new insights for potential use of L. gasseri as an alternative therapy for IBD, particularly in dietary supplementation.
Evidence Assessment: The evidence for L. gasseri in colitis or IBD is currently limited to animal models and mechanistic in vitro work. No adequately powered human RCTs in IBD populations have been identified in the peer-reviewed literature for this specific species. This area should be characterized as preclinical/preliminary.
5. Body Systems and Health Areas Associated with Lactobacillus gasseri
- Gastrointestinal tract: Maintenance of gut microbiota homeostasis; suppression of H. pylori; potential amelioration of diarrhea; support of intestinal barrier integrity; reduction of colonic inflammation (animal data).
- Metabolic system: Modest reductions in visceral and subcutaneous abdominal fat; body weight modulation in overweight/obese individuals.
- Female urogenital tract: Maintenance of vaginal microbiome; supportive role in bacterial vaginosis management; dysmenorrhea reduction in endometriosis (strain OLL2809).
- Immune system: Immunomodulation of the innate and adaptive systems.
- Gastric mucosa: Potential role for L. gasseri in maintaining gastric homeostasis and promoting healing of gastric lesions.
- Oral cavity: Normal inhabitant of the mouths of juveniles and adults, though clinical oral health applications are not yet established.
6. Dosage Forms and Dosages Reported in Studies
Typical adult doses range from 1–10 billion CFU/day; some RCTs used 1×10⁹ to 1×10¹⁰ CFU/day for 12 weeks.
The following dosages have been reported in specific identified clinical studies:
- L. gasseri SBT2055 for abdominal adiposity: The daily dose of L. gasseri SBT2055 in clinical trials was at the dose of 10¹¹ CFU. Trial duration was 12 weeks; delivered via fermented milk.
- L. gasseri BNR17 for obesity: In the 12-week RCT demonstrating significant VAT reduction, the high-dose BNR17 group achieved a mean difference of −21.6 cm² in visceral fat area compared to placebo (P = .012). The maximum ingestion based on the intended uses of L. gasseri BNR17 was noted to exceed 1.0 × 10¹¹ CFU/day.
- L. gasseri OLL2716 for H. pylori: Yogurt containing L. gasseri OLL2716 at ≥ 10⁹ CFU was used; 112 g of yogurt was consumed twice daily for 4 weeks (3 weeks pretreatment, 1 week concurrent with eradication therapy).
- L. gasseri OLL2716 for dyspepsia: 131 participants were randomly given L. gasseri OLL2716-containing yogurt or placebo yogurt once daily for 12 weeks.
- L. gasseri OLL2716 for delayed gastric emptying: Participants were assigned to ingest LG21 strain-containing yogurt or placebo yogurt for 12 weeks.
- Commercial supplement labeling (NIH DSLD): One labeled product contains 100 mg Lactobacillus gasseri CNCM I-5076 (6 billion micro-organisms) per capsule, recommended for adults at 2 capsules per day.
Clinical studies have used doses ranging from 1 to 10 billion CFUs daily for at least 12 weeks, though there is no established optimal dose. Typical trial durations have been eight to twelve weeks, with doses usually between 10⁸ and 10¹⁰ colony-forming units per day (CFU/day). There are few high-quality randomized data beyond three months, and long-term randomized trials are rare.
7. Safety Considerations and Interactions
7.1 General Safety and Regulatory Status
These bacteria are non-pathogenic and are 'generally regarded as safe' (GRAS) due to their long history of consumption in fermented foods in the human diet. Given the long history of consumption and human exposure, lactic acid bacteria are considered generally safe by the scientific community (Adams, 1999). The Lactobacillus genus, including Lactobacillus gasseri, retains an unchanged safety status under EFSA BIOHAZ Panel review (2022).
7.2 Commonly Reported Adverse Effects
L. gasseri is generally well-tolerated in healthy adults, with mild gastrointestinal effects such as bloating being most common. Generally safe for healthy adults; transient gas or bloating may occur in week 1–2. No adverse effects were observed during the course of one published placebo-controlled clinical study.
7.3 Risks in Vulnerable Populations
Individuals who are immunocompromised (including those with HIV/AIDS, undergoing chemotherapy, or taking immunosuppressive medications), those with central venous catheters, patients with severe acute pancreatitis, or those with compromised intestinal barrier function should exercise caution. There have been isolated case reports of Lactobacillus bacteraemia and endocarditis in immunocompromised patients, though such events are exceptionally uncommon.
People who are severely immunocompromised, those with indwelling central venous catheters, critically ill patients, and individuals with major surgical wounds or barrier compromise should avoid live bacterial supplements without clinician oversight.
There is currently limited evidence regarding the safety of L. gasseri supplementation during pregnancy and breastfeeding.
7.4 Rare Pathogenic Reports
In 2004, Lactobacillus gasseri was identified as a cause of Fournier's gangrene, a bacterial infection of the skin that affects the genitals and perineum. This represents an isolated case in the context of mixed-organism polymicrobial infection, and is not indicative of typical probiotic risk in healthy individuals.
7.5 Drug Interactions
There are no known interactions between L. gasseri and foods or drinks established in the current literature. Formal pharmacokinetic drug-drug interaction studies for L. gasseri as a dietary supplement have not been reported in the peer-reviewed literature. The use of L. gasseri as an adjunct to antibiotic triple therapy for H. pylori has been investigated in clinical trials without reported negative interactions with rabeprazole, amoxicillin, or clarithromycin at the doses studied. As a live microorganism, concurrent systemic antibiotic use may reduce its viability and efficacy, though direct evidence of harm from this interaction has not been documented for this species specifically.
7.6 Strain Specificity Caveat
Proper identification of probiotic microorganisms is essential because of the strain-specific nature of the health benefits associated with probiotic cultures and the intrinsic safety issues associated with erroneous identification. Not every product that claims to contain Lactobacillus gasseri will match what was tested in clinical research, as strain and dose matter because effects are strain-specific in probiotics.
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