This frog bacterium destroyed every cancer tumour in mice with just one dose

By Morgan Nwanguma

A naturally occurring bacterium discovered in the intestines of amphibians has shown extraordinary cancer-fighting potential, completely eliminating colorectal tumours in mice after a single treatment. Researchers say the findings could pave the way for a new generation of bacterial therapies capable of targeting a wide range of solid cancers.

The study, conducted by scientists at the Japan Advanced Institute of Science and Technology (JAIST) and published in Gut Microbes, demonstrates a novel approach to cancer treatment that employs living bacteria to directly attack tumours while simultaneously stimulating the body’s immune defenses.

Amphibian Gut Bacteria Show Powerful Anticancer Effects

Unlike previous research that focused on modifying the gut microbiome or using faecal microbiota transplants, the JAIST team isolated individual bacterial strains, cultured them in the laboratory, and administered them intravenously to evaluate their anticancer activity.

Researchers collected 45 bacterial strains from the intestines of Japanese tree frogs (Dryophytes japonicus), Japanese fire-bellied newts (Cynops pyrrhogaster), and Japanese grass lizards (Takydromus tachydromoides). After extensive screening, nine strains demonstrated promising anticancer properties. Among them, Ewingella americana emerged as the most effective.

One Dose Eradicated Colorectal Tumours

In mouse models of colorectal cancer, a single intravenous injection of E. americana completely eliminated tumours, achieving a 100 per cent complete response rate. The bacterium outperformed conventional treatments used as comparators in the study, including immune checkpoint inhibitors and the chemotherapy drug liposomal doxorubicin.

Although the results are currently limited to animal studies, the researchers believe they provide compelling evidence that naturally occurring bacteria could be developed into highly effective cancer therapies.

A Two-Pronged Assault on Cancer

The study revealed that E. americana combats cancer through two complementary mechanisms.

First, the bacterium directly attacks tumour tissue. As a facultative anaerobe, it can survive in both oxygen-rich and oxygen-poor environments, enabling it to flourish inside the oxygen-deprived regions commonly found within tumours. Once inside, bacterial numbers increased approximately 3,000-fold within 24 hours, leading to direct destruction of cancer cells.

Secondly, the bacterium activates the immune system. Its presence attracted key immune cells – including T cells, B cells and neutrophils – to tumour sites. These cells then released powerful inflammatory molecules such as tumour necrosis factor-alpha (TNF-α) and interferon-gamma (IFN-γ), enhancing immune activity and accelerating cancer cell death.

Why the Bacteria Prefer Tumours

One of the most remarkable findings was the bacterium’s ability to selectively accumulate inside tumours while largely avoiding healthy tissues.

Researchers believe several tumour-specific characteristics contribute to this targeting ability. Tumours often contain low-oxygen environments that support bacterial growth. Many cancer cells also produce high levels of CD47, a protein that suppresses immune activity and may create a more favourable environment for bacterial survival.

In addition, tumour blood vessels are unusually leaky, making it easier for circulating bacteria to enter cancerous tissue. Altered tumour metabolism may also provide nutrients that promote bacterial growth.

Together, these factors enable E. americana to concentrate where cancer is present while sparing normal organs.

Encouraging Safety Profile

The research team also reported favourable safety results.

The bacteria were rapidly cleared from the bloodstream, with a half-life of about 1.2 hours, and became undetectable within 24 hours. Importantly, no bacterial colonisation was found in healthy organs such as the liver, spleen, lungs, kidneys or heart.

The treatment caused only mild and temporary inflammation, which resolved within 72 hours. During a 60-day monitoring period, researchers observed no signs of chronic toxicity or long-term adverse effects.

Potential Beyond Colorectal Cancer

While the current study focused on colorectal cancer, the researchers believe the approach could be extended to other solid tumours, including breast cancer, pancreatic cancer and melanoma.

Future studies will explore ways to optimise treatment, including adjusting dosing schedules and delivering the bacteria directly into tumours. Scientists also plan to investigate whether E. americana can enhance the effectiveness of existing chemotherapy and immunotherapy treatments when used in combination.

Beyond its implications for cancer therapy, the discovery highlights the untapped medical potential hidden within nature’s biodiversity. Researchers say exploring microorganisms found in wildlife may uncover entirely new classes of treatments for diseases that remain difficult to manage with current therapies.

If future studies confirm these results in humans, bacteria-based therapies could become a powerful new weapon in the fight against cancer, offering hope to patients with some of the most challenging forms of the disease.

Glossary

· Facultative Anaerobic Bacteria: Bacteria capable of growing in both oxygen rich and oxygen depleted environments, allowing them to selectively multiply in the low oxygen conditions found inside tumours.

· Complete Response (CR): Complete disappearance of detectable tumours following treatment.

· Immune Checkpoint Inhibitor: Drugs that remove the signals cancer cells use to suppress the immune system, allowing T cells to attack tumours more effectively.

· CD47: A protein on the surface of cells that sends a “don’t eat me” signal to the immune system. Many cancer cells produce large amounts of CD47 to avoid immune attack.

The study was aided by the Japan Society for the Promotion of Science (JSPS) KAKENHI Grant-in-Aid for Scientific Research (A) (Grant No. 23H00551), JSPS KAKENHI Grant-in-Aid for Challenging Research (Pioneering) (Grant No. 22K18440), the JSPS Programme for Forming Japan’s Peak Research Universities（J-PEAKS） (Grant No. JPJS00420230006), the Japan Science and Technology Agency (JST) Programme for Co-creating Startup Ecosystem (Grant No. JPMJSF2318), and JST SPRING (Grant No. JPMJSP2102).