Yogurt-derived probiotic bacteria killed colon cancer cells in lab dish tests

Colorectal cancer is projected to affect more than 2.2 million people worldwide each year by 2030, and probiotics have drawn growing interest as a low-risk, adjunct approach to cancer research. A new laboratory study out of Iran adds a small but concrete data point: extracts made from Lactobacillus bacteria isolated from traditional, homemade yogurt killed human colorectal cancer cells in a dish, with the effect growing stronger at higher doses. The work stops well short of anything close to a treatment, but it shows one more way ordinary probiotic bacteria might be put to use against cancer cells.

Key Takeaways:

• Cytoplasmic extracts (the internal contents of bacterial cells) from three Lactobacillus strains isolated from traditional Iranian yogurt reduced the viability of HT-29 human colorectal cancer cells in a dish, with more than 70% of cells losing viability at the highest dose tested.
• One strain, Lactobacillus fermentum (AGR1487), was the most potent, killing cancer cells even at the lowest concentration tested and reaching its half-maximal effect (IC50) at roughly 1.2 to 1.4 mg/mL.
• This is lab-dish (in vitro) work only; it was never tested in a living animal or person, and it has not been shown to work inside a real gut.
• The finding adds an incremental data point to an already well-studied area of Lactobacillus-versus-cancer-cell research rather than a breakthrough.

Yogurt-Derived Lactobacillus Extracts Reduced Colon Cancer Cell Viability in a Dish

Researchers isolated bacteria from 21 samples of traditional, non-industrial yogurt collected from households and local dairy markets near Isfahan, Iran, and identified 8 distinct Lactobacillus isolates using genetic sequencing (16S rRNA sequencing, a standard method for identifying bacterial species). From those, they selected three strains for testing, Lactobacillus casei (MGB0470), Lactobacillus casei (LcA) and Lactobacillus fermentum (AGR1487), and exposed HT-29 human colorectal cancer cells in a dish to cytoplasmic extracts (the fluid and dissolved contents released when bacterial cells are broken open) from each strain at concentrations from 0.5 to 2 milligrams per milliliter. All three extracts reduced cancer cell viability in a dose-dependent way, meaning more extract killed more cells, and at the highest dose tested, viability dropped by more than 70%, according to the study published in the Journal of Shahrekord University of Medical Sciences. The result echoes a related finding in which a related Lactobacillus strain slowing colorectal tumor growth was reported by a separate research group.

Why Colorectal Cancer Research Matters to a Broad Group of Readers

Colorectal cancer is the third leading cause of cancer death worldwide, and its incidence is projected to keep climbing, particularly in regions undergoing rapid dietary and lifestyle change. For readers already paying attention to gut health, whether because of a family history of colorectal cancer, a personal digestive condition, or general interest in how diet and probiotics intersect with disease risk, this study adds to a growing body of lab research asking whether everyday probiotic bacteria, the kind already found in yogurt, could eventually support cancer treatment or prevention strategies, an area a recent review has also examined by asking whether probiotic-rich yogurt and colorectal cancer risk are linked in humans.

How the Study Was Designed and What It Actually Tested

This was a controlled laboratory (in vitro) experiment, not a clinical study. After identifying and genetically confirming the three Lactobacillus strains, the researchers broke open bacterial cells using repeated freeze-thaw cycles and sonication (high-frequency sound waves) to release their cytoplasmic contents, then applied the resulting extracts directly to HT-29 cells, a standard laboratory human colorectal cancer cell line, growing in culture dishes. Cell viability after 24 hours of exposure was measured using the MTT assay, a common lab test that estimates how many cells are still metabolically active, a method also used in other work exploring a key cancer cell signaling pathway affected by Lactobacillus species. Lactobacillus fermentum (AGR1487) proved the most potent of the three, killing a significant share of cancer cells even at the lowest dose tested (0.5 mg/mL) and reaching its IC50 (the concentration needed to kill half the cells) between roughly 1.2 and 1.4 mg/mL.

What This Could Mean, and What It Doesn't Mean Yet

This finding does not mean eating yogurt kills colon cancer cells in your body, and the researchers did not test that. The extracts were applied directly to cancer cells in a dish, at concentrations and in a form that bear little resemblance to what happens when yogurt or its bacteria pass through the human digestive tract. The authors frame their work as an early step, worth following up with animal studies and eventually human research, not as evidence that any specific yogurt or probiotic product has anticancer effects. Readers interested in colorectal cancer prevention should continue to rely on established, proven approaches, such as regular screening and a high-fiber diet, rather than treating probiotic yogurt as a cancer-fighting intervention.

Why This Is an Early, Incremental Finding, Not a Breakthrough

The study was conducted entirely in vitro, using a single cancer cell line (HT-29), so the results have not been confirmed in a living animal or a person, and it remains unknown whether these extracts would survive digestion, reach the colon intact, or behave the same way inside the complex environment of the human gut. The researchers also did not identify which specific molecules within the cytoplasmic extracts are responsible for the cell-killing effect, so the active compounds remain uncharacterized. The broader research area, testing Lactobacillus and other probiotic-derived extracts against colorectal cancer cell lines, is already well established, as shown by another in vitro probiotic study using a different strain combination, and this study adds one more strain comparison to that existing body of work rather than a new mechanism or breakthrough.

What Comes Next for This Line of Research

The study's authors call for follow-up work to identify the specific bioactive molecules driving the cytotoxic effect, testing in additional colorectal cancer cell lines beyond HT-29, and eventually moving into animal models to see whether the effect holds up in a living digestive system before any human relevance can be assessed. Until those steps happen, the practical takeaway for now is that this remains a laboratory finding pointing toward a promising research direction, not a validated anticancer strategy.

Common Questions

Does this mean yogurt can help prevent or treat colon cancer? Not based on this study. The researchers tested purified bacterial extracts directly on cancer cells in a lab dish, not whole yogurt consumed by a person, so no conclusion about eating yogurt can be drawn from these results.

What is a cytoplasmic extract? It is the internal fluid and dissolved contents released when a bacterial cell is broken open in the lab, here obtained from Lactobacillus bacteria using freeze-thaw cycles and sound-wave disruption.

Which strain worked best in this study? Lactobacillus fermentum (AGR1487), isolated from traditional yogurt, showed the strongest cell-killing effect among the three strains tested, working even at the lowest dose used.

Has this been tested in animals or people? No. This was an in vitro (lab dish) study only; the effect has not been tested in a living animal or a human, and the authors say animal studies are a needed next step.

References

1. Arezoo Haghighi, Mozhgan Ghiasian, Fereshte Ghandehari (2026). Cytotoxic Effects of Cytoplasmic Extracts from Traditional Yogurt-derived Lactobacillus Strains on HT-29 Human Colorectal Cancer Cells. Journal of Shahrekord University of Medical Sciences. https://doi.org/10.34172/jsums.1125
2. Wei Lyu, Lu Chen, De‐Feng Li, et al. (2025). Lactobacillus johnsonii‐FM1 modulates gut microbiota and secretes anticancer metabolite vanillic acid to inhibit colorectal tumorigenesis. iMetaOmics. https://doi.org/10.1002/imo2.70050
3. Biplab Adhikari (2026). Can probiotic-rich yogurt help prevent colorectal cancer in humans?. Cancer Pathogenesis and Therapy. https://doi.org/10.1016/j.cpt.2025.06.002
4. Roya Ghanavati, Abolfazl Akbari, Fahime Mohammadi, et al. (2020). Lactobacillus species inhibitory effect on colorectal cancer progression through modulating the Wnt/β-catenin signaling pathway. Molecular and Cellular Biochemistry. https://doi.org/10.1007/s11010-020-03740-8
5. Oana Budu, Christian Banciu, Iulia Pinzaru, et al. (2022). A Combination of Two Probiotics, Lactobacillus sporogenes and Clostridium butyricum, Inhibits Colon Cancer Development: An In Vitro Study. Microorganisms. https://doi.org/10.3390/microorganisms10091692