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A surprising new study reports that a bacterium living in the gut of Japanese tree frogs can completely eliminate cancer tumours in mice after just a single dose. Researchers at the Japan Advanced Institute of Science and Technology (JAIST) discovered that Ewingella americana, when injected into the bloodstream, wiped out colorectal tumours in every treated mouse—performing better than established cancer treatments such as chemotherapy (doxorubicin) and immune checkpoint therapy (anti-PD-L1). The work was published in the journal Gut Microbes.
The team turned to amphibians and reptiles because these animals rarely develop cancer despite long lifespans, extreme cellular stress, and exposure to pathogens. Suspecting a role for microbes, the researchers screened 45 bacterial strains isolated from frogs, newts, and lizards. Nine showed anti-tumour effects, but E. americana stood out for its exceptional potency and selectivity. When administered intravenously, the bacterium homed in on tumours, rapidly multiplying in the low-oxygen environment typical of solid cancers while leaving healthy tissues untouched.
The bacterium attacks cancer in two ways. First, it directly kills tumour cells by secreting toxins inside the tumour. Second, its presence sparks a powerful immune response, flooding tumours with immune cells such as T cells, B cells, and neutrophils. Remarkably, mice treated with a single dose not only cleared their tumours but also developed long-lasting immune memory: when later re-exposed to cancer cells, none formed new tumours.
Safety tests were equally encouraging. The bacteria were cleared from the bloodstream within 24 hours, caused only temporary inflammation, and showed no signs of long-term toxicity or organ damage. They were also sensitive to antibiotics, offering an added safety net. While these results are still limited to mice, the researchers see this as a proof-of-concept for a new class of cancer treatments based on naturally occurring microbes. Next, they plan to test the approach in other cancers, including breast, pancreatic, and melanoma, and explore how it might complement existing cancer therapies.
