From Confusion to Clarity: The Taxonomic Separation
For many years, microbiologists grouped Lactobacillus reuteri with Lactobacillus fermentum, leading to historical confusion. The misconception was primarily due to their similar characteristics as obligate heterofermentative lactobacilli, meaning they produce lactic acid, ethanol, and carbon dioxide from sugars. In the 1960s, further research identified distinct biotypes, with one eventually becoming the basis for a new, separate species. By 1980, sufficient genetic and phenotypic differences were identified to formally propose Lactobacillus reuteri as its own species. This distinction was crucial for accurately studying the unique properties of each probiotic.
The Modern Taxonomic Update: Limosilactobacillus
Compounding the historical reclassification, a major taxonomic overhaul in April 2020 resulted in the division of the Lactobacillus genus into 25 new genera. Under this new system, both L. fermentum and L. reuteri were moved to the new genus Limosilactobacillus, a name derived from 'limus' (slime), reflecting their ability to form biofilms.
This means their correct scientific names are now Limosilactobacillus fermentum and Limosilactobacillus reuteri. It is important to remember this when reading scientific literature, as older studies will still refer to them under the former Lactobacillus classification.
Comparison of L. fermentum and L. reuteri
While closely related, their specific genetic makeup leads to different metabolic activities and health benefits. A comparative genomic study highlights a striking difference in their guanine-cytosine (GC) content and gene clusters, underscoring their distinct evolutionary paths.
Unique Probiotic Mechanisms
L. reuteri is particularly known for its ability to produce a broad-spectrum antimicrobial compound called reuterin. This metabolite is produced during the fermentation of glycerol and helps L. reuteri inhibit the growth of harmful bacteria and fungi. In contrast, L. fermentum does not produce reuterin, but instead relies on different mechanisms, such as producing other antimicrobial peptides and organic acids like lactic, acetic, and succinic acids.
Distinct Health Benefits
Research has explored the different applications of these two probiotic species. Clinical evidence suggests that strains of L. reuteri, particularly DSM 17938, are effective in reducing symptoms of infantile colic, while strains of L. fermentum have shown promising anti-inflammatory and immunomodulatory properties in preclinical studies.
Comparison Table: L. fermentum vs. L. reuteri
| Feature | Limosilactobacillus fermentum | Limosilactobacillus reuteri |
|---|---|---|
| Historical Classification | Originally included L. reuteri as a biotype. | Mistakenly grouped under L. fermentum until 1980. |
| Taxonomic Genus | Limosilactobacillus. | Limosilactobacillus. |
| Antimicrobial Production | Produces various organic acids and bacteriocins. | Produces reuterin, a powerful broad-spectrum antimicrobial. |
| Genetic Profile | Distinctly different genomic features, including higher GC content. | Unique gene cluster for reuterin and B12 synthesis. |
| Primary Benefits | Anti-inflammatory properties, improved liver function, and antioxidative effects. | Reduced infantile colic, alleviated stomach pain, and gut motility improvement. |
| Example Applications | Adjunctive therapy for diabetes and liver function. | Treating infantile colic and managing H. pylori side effects. |
Other Key Differences and Considerations
Beyond their core functions, research continues to reveal more about their specific applications:
- In Vitro Studies and Strain Specificity: It is important to note that many of these benefits are strain-specific. A 2007 comparative study found that L. fermentum demonstrated more effective anti-inflammatory properties than L. reuteri in a rat colitis model, showcasing how specific strain performance can vary. For example, the L. reuteri strain ATCC 6475 has been shown to reduce bone loss in mice, an effect not extensively documented for L. fermentum.
- Influence on the Microbiome: Both probiotics impact the overall gut flora composition, but their specific influence can differ based on host health, dosage, and other factors. L. reuteri has been observed to influence the composition of the gut microbiota in infants with colic, while L. fermentum contributes to overall microbiome diversity.
- Safety and Tolerance: Both are generally considered safe and well-tolerated when used as probiotics. However, as with any supplement, individual reactions can occur, and it is important to consult a healthcare provider for personalized advice.
- Commercial Applications: The differing properties mean they are used for distinct commercial purposes. L. reuteri is often included in products targeting infant health and colic, while specific strains of L. fermentum are used in functional foods for metabolic support.
Conclusion
In conclusion, the answer to the question "Is Lactobacillus fermentum the same as reuteri?" is a definitive no. While historically and phylogenetically related, these are distinct species, now both classified under the genus Limosilactobacillus. Key differentiating factors include the production of unique antimicrobial compounds like reuterin by L. reuteri and differences in their therapeutic applications, particularly in treating infantile colic (L. reuteri) versus providing anti-inflammatory and metabolic support (L. fermentum). The ongoing taxonomic and genetic research continues to reveal that even closely related probiotics possess unique mechanisms that result in distinct health benefits, highlighting the importance of understanding the specific strain and species when considering probiotic supplementation. For more detailed insights into probiotic mechanisms, the National Institutes of Health provides comprehensive research.
Note: The effectiveness and optimal application of these probiotics are strain-dependent. Always consult with a healthcare professional before starting any new supplement.
