Frog-gut bacterium wipes out tumors in mice — but it's one preclinical study

A peer-reviewed paper in Gut Microbes reports that Ewingella americana, a naturally occurring bacterium isolated from amphibian and reptile gut microbiomes, eliminated colorectal tumors in 100% of treated mice after a single intravenous dose, with no recurrence on re-challenge and no measurable toxicity. The study frames it as outperforming both doxorubicin chemotherapy and anti–PD-L1 checkpoint blockade. The proposed mechanism is dual-action: as a facultative anaerobe the bacterium homes to the low-oxygen tumor core (researchers cite a ~3,000-fold jump in intratumoral bacterial load within 24 hours), kills tumor cells directly, and triggers a broad immune response marked by T-cell, B-cell, and neutrophil infiltration and spikes in TNF-α and IFN-γ. It was reportedly cleared from circulation within a day while staying localized in tumor tissue.