Streptococcus thermophilus survival in the gut and identification problems
What it found
Studies in people disagree on whether Streptococcus thermophilus survives the trip through the gut, and the review authors say the lab methods used to identify it in stool often cannot tell it apart from a closely related mouth bacterium.
The authors conclude that no test yet can reliably distinguish the two in stool samples.
What they found
Studies in people
Survival in the gut
Some studies in people found that Streptococcus thermophilus could be recovered from stool after eating yogurt or probiotic products, while one study found none. The authors say these differences may come from the strains used, how they were grown, or the number of live cells given.
Other findings
Misidentification with S. salivarius
Streptococcus thermophilus is genetically very similar to Streptococcus salivarius, a common mouth and gut bacterium. The review says that in most studies, the methods used to identify Streptococcus thermophilus from stool were not specific enough to rule out misidentification with S. salivarius.
Problems with lab methods
Many DNA-based tests used to detect Streptococcus thermophilus in stool, such as those targeting the 16S rDNA or lacZ genes, cannot reliably tell it apart from S. salivarius. The authors say that to date there are no taxonomically correct assays that can unambiguously identify Streptococcus thermophilus in a stool sample.
Metagenomics studies
In some studies that looked at gut bacteria using metagenomics, the genome of S. salivarius was not included as a reference, so the prevalence of Streptococcus thermophilus may have been overestimated. The authors say this can lead to wrong conclusions about whether Streptococcus thermophilus lives in the human gut.
What the authors conclude
“In light of the scientific literature cited we can, therefore, conclude that to date there are no taxonomically correct assays that allow to unambiguously identify S. thermophilus strains and distinguish them from those belonging to S. salivarius in a stool sample.”
Also in their conclusions
- They conclude that the probiotic status of S. thermophilus has been in debate for decades and that accurate taxonomic identification is a paramount issue to be validated for the compliance of probiotic food and supplement products.
- They advise that guidelines should recommend a proper study design based on a double-blind, placebo-controlled crossover design, an appropriate washout period, and the use of species-specific plate culture methods and/or strain-specific molecular tools to correctly identify the orally administered probiotic.
- They also suggest that subjects showing a positive detection of the probiotic strain in fecal samples during the run-in or placebo period should be excluded from intervention studies.
How it was done
The authors wanted to check the scientific evidence behind the probiotic status of Streptococcus thermophilus, because the studies that tested whether it survives the human gut have given contradictory results.
They reviewed published studies that gave Streptococcus thermophilus to people, usually in yogurt or probiotic products, and then tried to recover and identify the bacterium from stool samples. They also examined the laboratory methods used for identification and the genetic similarity between Streptococcus thermophilus and Streptococcus salivarius.
What it can’t tell you
- The review cannot show whether Streptococcus thermophilus actually survives the human gut, because the studies it examined used methods that may not have identified the bacterium correctly.
- It cannot show whether any health benefits seen in people are due to Streptococcus thermophilus itself, since the products tested often contained multiple strains.
- It cannot show what happens in the gut from the genetic comparisons done in the lab.
Who paid
- Conflicts
- The authors declare no conflict of interest.
- Authors work at
- University of Milan, Italy
The paper
- Title
- Streptococcus thermophilus : To Survive, or Not to Survive the Gastrointestinal Tract, That Is the Question!
- Type
- ReviewThe authors read earlier studies and describe what they found. It isn’t a new study.
- Evidence
- Studies in people
- Summarised from
- Full text
- Licence
- CC BY. Words in quotation marks are the authors’; the rest is our summary.
- Cite
- Martinović A, Cocuzzi R, Arioli S, Mora D (2020). Streptococcus thermophilus : To Survive, or Not to Survive the Gastrointestinal Tract, That Is the Question!. Nutrients. doi:10.3390/nu12082175Free full textPubMed 32708008DOI
Summary written 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error