Scientists at the Japan Advanced Institute of Science and Technology (JAIST) have identified a naturally occurring bacterium from the intestines of Japanese tree frogs (Dryophytes japonicus) that demonstrated remarkable anticancer activity in mice.
The findings, published in Gut Microbes, introduce a new approach to cancer treatment that uses living bacteria to directly target tumors rather than simply altering the gut microbiome.
The team collected 45 bacterial strains from the intestines of Japanese tree frogs, Japanese fire belly newts, and Japanese grass lizards. After screening for anticancer activity, Ewingella americana from the tree frog produced the strongest results.
Single Treatment Eliminated Tumors
In a mouse model of colorectal cancer, a single intravenous dose of E. americana completely eliminated tumors, producing a 100% complete response rate. The treatment outperformed standard therapies including immune checkpoint inhibitors and chemotherapy.
The researchers emphasize these findings are limited to mice, but believe the results provide an encouraging proof of concept for developing new bacterial cancer therapies.
Dual Attack Mechanism
The bacterium fights cancer through two complementary mechanisms. First, it directly attacks tumors — as a facultative anaerobic bacterium, it thrives in oxygen-deprived regions common inside tumors, multiplying roughly 3,000-fold within 24 hours after treatment.
Second, it stimulates the immune system. Its presence attracts T cells, B cells, and neutrophils into tumors, which release inflammatory signaling molecules including TNF-α and IFN-γ, strengthening the immune response and promoting cancer cell death.
Remarkable Tumor Specificity
One of the most striking findings was that E. americana accumulated almost exclusively inside tumors and did not colonize healthy organs. Factors contributing to this include the low-oxygen environment inside tumors, the CD47 protein that suppresses local immune activity, leaky tumor blood vessels, and tumor-specific metabolic changes that provide bacterial nutrients.
The bacteria were cleared from the bloodstream with a half-life of approximately 1.2 hours and became undetectable within 24 hours. No colonization was detected in healthy organs, and the treatment caused only mild, temporary inflammation that returned to normal within 72 hours.
Future Directions
The study establishes proof of concept for using naturally occurring bacteria as cancer therapy. Future research will examine application to additional solid tumors including breast, pancreatic, and melanoma. Researchers will also investigate whether E. americana works even better when combined with existing chemotherapy or immunotherapy.
