Frog Gut Bacterium Ewingella americana Achieves 100% Tumor Elimination in Mice with a Single Dose
Key Insights
Japanese researchers discovered that Ewingella americana (search), a bacterium from Japanese tree frog intestines, achieved complete tumor elimination in a mouse model of colorectal cancer (search) with a single intravenous dose.
The treatment produced a 100% complete response rate, dramatically outperforming standard therapies including immune checkpoint inhibitors and liposomal doxorubicin.
The bacterium employs a dual mechanism: direct tumor attack through rapid intratumoral proliferation and immune system activation via T cell, B cell, and neutrophil recruitment.
A research team led by Professor Eijiro Miyako at Japan's Advanced Institute of Science and Technology has demonstrated that a naturally occurring bacterium isolated from the intestines of the Japanese tree frog can eliminate colorectal cancer (search) tumors in mice with a single intravenous dose, achieving a 100% complete response rate.
The bacterium, Ewingella americana (search), was one of 45 bacterial strains isolated from the intestines of Japanese tree frogs, Japanese fire belly newts (Cynops pyrrhogaster), and Japanese grass lizards (Takydromus tachydromoides). Through systematic screening, nine strains demonstrated anti-tumor effects, with E. americana exhibiting the most exceptional therapeutic efficacy.
"These findings suggest that gut microbiomes of lower vertebrates harbor numerous uncharacterized bacterial species with exceptional therapeutic potential," the authors wrote in their paper published in the journal Gut Microbes. "Our study underscores the critical importance of microbial biodiversity in advancing cancer treatment strategies."
Dual Mechanism of Action
The bacterium fights cancer through two complementary mechanisms. First, as a facultative anaerobic bacterium, E. americana thrives in both oxygen-rich and oxygen-poor environments, allowing it to multiply selectively inside the oxygen-deprived regions commonly found within tumors. The bacterial population increased by approximately 3,000-fold within 24 hours after treatment, directly damaging cancer cells.
Second, the bacterium stimulates the immune system. Its presence attracted T cells, B cells, and neutrophils into tumors, where these immune cells released inflammatory signaling molecules including TNF-α and IFN-γ, strengthening the immune response and promoting cancer cell death.
Tumor-Specific Targeting
One of the most striking findings was that E. americana accumulated almost exclusively inside tumors and did not colonize healthy organs. The researchers attribute this tumor specificity to several factors: the low-oxygen tumor microenvironment, cancer cell production of the CD47 (search) protein that suppresses local immune activity, unusually leaky tumor blood vessels, and tumor-specific metabolic changes that provide nutrients supporting bacterial growth.
Superior Efficacy Compared to Standard Therapies
In a mouse model of colorectal cancer (search), a single intravenous administration of E. americana dramatically surpassed the efficacy of current standard therapies, including immune checkpoint inhibitors (anti-PD-L1 antibody (search)) and liposomal doxorubicin chemotherapy.
Favorable Safety Profile
The research team conducted extensive safety evaluations. The bacteria were rapidly cleared from the bloodstream, with a half-life of approximately 1.2 hours, becoming completely undetectable within 24 hours. No bacterial colonization was detected in healthy organs, including the liver, spleen, lungs, kidneys, or heart. The treatment caused only mild, transient inflammatory responses that normalized within 72 hours. During a 60-day extended observation period, researchers found no evidence of chronic toxicity.
Future Directions
The study establishes proof of concept for using naturally occurring bacteria as a cancer therapy. Future research will expand to evaluate efficacy in other cancer types, including breast cancer (search), pancreatic cancer (search), and melanoma (search). The team also plans to optimize treatment methods through dose fractionation and intra-tumoral injection, and will investigate potential synergistic effects with existing immunotherapy and chemotherapy.
The research was supported 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 Program for Forming Japan's Peak Research Universities (J-PEAKS) (Grant No. JPJS00420230006), the Japan Science and Technology Agency (JST) Program for Co-creating Startup Ecosystem (Grant No. JPMJSF2318), and JST SPRING (Grant No. JPMJSP2102).