Streptococcus thermophilus and Lactococcus lactis in the human gut
What it found
In gut bacteria samples from 10,000 healthy adults, Streptococcus thermophilus was found in 16.3% and Lactococcus lactis in 4.6%.
In lab tests, both strains survived gut conditions and used many sugars.
What they found
Studies in people
How common in people
Among gut bacteria from 10,000 healthy adults, Streptococcus thermophilus was found in 16.3% and Lactococcus lactis in 4.6%. These were the most common lactic acid bacteria from food.
Staying in the gut
In 35 people tracked over seven days, S. thermophilus stayed present in seven people across more than 85% of samples. L. lactis stayed stable in only four people.
Animal and lab studies
Sugar use in lab
In lab tests, both strains grew well on 14 and 20 common gut sugars, respectively. S. thermophilus grew better on nine sugars including inulin and sucrose, while L. lactis grew better on glucose and maltose.
Lactose breakdown
In lab tests, S. thermophilus made more lactic acid from lactose but left galactose behind. L. lactis used up all the galactose with less acid. When grown together, L. lactis used the leftover galactose and kept acid levels moderate.
Gut survival in lab
In lab tests, both strains survived harsh conditions well. Over 85% of L. lactis and over 95% of S. thermophilus survived high salt. They also survived bile salts and acid at pH 3, with survival rates of 86% and 92%.
Sticking to gut cells
In lab tests, both strains stuck to human gut cells. L. lactis had a higher adhesion index than S. thermophilus.
Gene activity on gut cells
When grown on human gut cell layers in the lab, L. lactis turned up 104 genes and S. thermophilus turned up 102 genes compared to growing alone. S. thermophilus turned up genes for making surface sugars that may help it stick.
What the authors conclude
- They say the two strains are ecologically adapted to survive and interact in the human gut.
- They note that S. thermophilus is the most common food-related lactic acid bacterium in the gut and is linked to beneficial butyrate-producing bacteria.
- They conclude that these strains are promising candidates for future studies in people.
How it was done
The authors wanted to understand how lactic acid bacteria from food interact with the human gut and other gut bacteria, since little was known about this.
They looked at gut bacteria data from 10,000 healthy adults and tracked 35 people over seven days. They then grew two chosen strains in the lab and tested their ability to use 33 different sugars, survive gut-like stress, stick to human gut cells, and change their gene activity when exposed to those cells.
What it can’t tell you
- This study used lab tests and gut bacteria data. It cannot show what would happen if people ate these strains as a probiotic.
- The link between S. thermophilus and butyrate-producing bacteria is a correlation, so it cannot show that one causes the other.
Who paid
- Funding
- Funded by Ministero della Ricerca e dell'Università; Italian Ministry of Health (from the PubMed record).
- Conflicts
- The authors declare no conflict of interest.
- Authors work at
- University of Parma, Italy; University of Modena and Reggio Emilia, Italy
The paper
- Title
- Host interactions of Lactococcus lactis and Streptococcus thermophilus support their adaptation to the human gut microbiota
- Type
- Study
- Evidence
- Studies in people · animals · lab
- Summarised from
- Full text
- Licence
- CC BY. Words in quotation marks are the authors’; the rest is our summary.
- Cite
- Lugli GA, Argentini C, Tarracchini C, et al (2025). Host interactions of Lactococcus lactis and Streptococcus thermophilus support their adaptation to the human gut microbiota. Applied and environmental microbiology. doi:10.1128/aem.01547-25Free full textPubMed 41186403DOI
Summary written 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error