Frog Gut Bacterium Ewingella Americana Eliminates Colorectal Tumors in Mice With a Single Dose, JAIST Study Finds
A single intravenous dose of the frog-gut bacterium Ewingella americana produced complete tumor regression in every treated mouse in a colorectal cancer model, outperforming anti-PD-L1 immunotherapy and chemotherapy, JAIST researchers report in Gut Microbes.
Overview
A bacterium isolated from the intestines of Japanese tree frogs eliminated tumors in every treated mouse in a colorectal cancer model after a single intravenous dose, according to a study led by researchers at the Japan Advanced Institute of Science and Technology (JAIST) and highlighted by ScienceDaily on July 10, 2026. The findings, published in the journal Gut Microbes, describe a bacterium called Ewingella americana that both directly kills cancer cells and activates the host immune system, a two-pronged mechanism the research team says outperformed standard immunotherapy and chemotherapy in the mouse model tested.
What We Know
The research, led by Prof. Eijiro Miyako at JAIST, screened nine bacterial strains isolated from the intestines of amphibians and a reptile — Japanese tree frogs (Dryophytes japonicus), Japanese fire-belly newts (Cynops pyrrhogaster), and Japanese grass lizards (Takydromus tachydromoides) — for anticancer activity, according to the study’s abstract in Gut Microbes. Among the isolates, E. americana, recovered from the tree frogs, showed the strongest and most selective activity against tumors, according to SciTechDaily.
In mice implanted with Colon-26 colorectal carcinoma cells, a single intravenous injection of the bacterium — administered via the tail vein once tumors reached roughly 200 cubic millimeters — produced a 100 percent complete-response rate across all treated animals, according to the Gut Microbes paper. By comparison, treatment with an anti-PD-L1 checkpoint-inhibitor antibody achieved only one complete response, and the chemotherapy drug liposomal doxorubicin failed to consistently eradicate tumors, the paper states. ScienceDaily and MedicalXpress both reported that the bacterial treatment outperformed both of those standard therapies in the study.
The researchers describe a dual-action mechanism: the bacterium selectively accumulates in the oxygen-poor tissue at the center of tumors, where it directly kills cancer cells, while also triggering an immune response that recruits T cells, B cells, and neutrophils, according to the Gut Microbes paper. That immune activation includes the release of inflammatory signaling molecules TNF-α and IFN-γ, according to both ScienceDaily and MedicalXpress. Bacterial levels inside tumors rose by approximately 3,000-fold in the first 24 hours after injection, reflecting the strain’s selective tumor-targeting ability, the paper reports.
Mice that were cured after treatment also developed lasting immunity: when researchers re-injected cancer cells into the cured animals, none of the ten mice developed new tumors, compared with all ten untreated control mice, which developed tumors as expected, according to the Gut Microbes paper. The paper describes this immunological memory as persisting beyond 60 days, and reports that a single bacterial dose extended overall mouse survival by at least 30 days compared with untreated controls.
On safety, the bacterium cleared from the bloodstream quickly, with a half-life of approximately 1.2 hours and no detectable bacteria remaining after 24 hours, according to both ScienceDaily and SciTechDaily. The Gut Microbes paper reports no bacterial colonization of healthy organs and no significant differences in blood or tissue markers between treated mice and untreated controls, beyond mild, temporary inflammation that resolved within 72 hours, according to ScienceDaily.
The study marks a departure from most prior gut-microbiome cancer research, which has focused on altering the overall composition of gut bacteria through diet, probiotics, or fecal transplants. Instead, the JAIST team isolated a single bacterial strain, cultured it in the laboratory, and delivered it directly into the bloodstream to attack tumors, according to ScienceDaily.
What We Don’t Know
The results come entirely from a mouse model using one cancer cell line; the bacterium has not been tested in humans. The Gut Microbes paper authors describe a narrow therapeutic window that will require careful management for any future clinical use, recommending strategies such as splitting doses to avoid peak systemic bacterial load and pairing treatment with intensive monitoring and antibiotics as a fail-safe, since the strain remains susceptible to standard antimicrobial drugs.
Researchers say next steps include testing the bacterium against other solid tumor types, including breast, pancreatic, and melanoma cancers, and exploring combination therapies alongside existing cancer treatments, according to ScienceDaily. An oral delivery method, which the Gut Microbes paper says would require developing protective formulations such as enteric coatings, has not yet been developed. No timeline for human trials has been announced.