Scientists Develop Cancer-Eating Bacteria to Attack Tumors from the Inside

Scientists at the University of Waterloo are developing an experimental cancer treatment that uses cancer-eating bacteria to attack tumors from the inside, offering a potential new option for cancers that resist conventional therapies.

The approach focuses on solid tumors, which often contain dense inner cores with little or no oxygen. These low-oxygen regions are difficult for chemotherapy, radiation, and immune-based treatments to reach. As a result, cancer cells can survive deep inside the tumor and later cause the disease to return.

Bacteria spores migrating to the tumor site

Researchers are working with bacterial spores that naturally thrive in oxygen-free environments. Once introduced into the body, the spores migrate into the tumor’s core, where nutrients are plentiful, and oxygen is scarce.

Dr. Marc Aucoin, a professor of chemical engineering involved in the work, said the bacteria take advantage of the tumor’s internal conditions. As the microbes multiply, they consume nutrients and begin breaking down tumor tissue from within.

Instead of attacking cancer from the outside, the method targets the tumor’s most protected area. Limited blood flow in the core often shields cancer cells from treatment. By colonizing this space, the bacteria may help eliminate cells that other therapies fail to reach.

Soil bacterium exploits oxygen-free tumor cores

At the center of the strategy is Clostridium sporogenes, a bacterium commonly found in soil. The microbe can survive only in environments that contain no oxygen at all. That trait makes it especially suited for the inner regions of solid tumors, which often lack oxygen and contain large numbers of dead cells.

Inside these oxygen-free zones, the bacteria can multiply and spread. Researchers say the tumor’s core provides both the conditions and nutrients the microbe needs to grow.

However, the strategy comes with a challenge. As the bacteria expand outward from the tumor’s center, they encounter small amounts of oxygen near the edges. Exposure to oxygen causes the microbes to die before they can fully destroy the cancer.

Genetic modification improves bacterial survival

To address this limitation, researchers genetically modified the bacteria. They inserted a gene taken from a related species that can better tolerate oxygen. The added gene allows the engineered microbes to survive longer as they move closer to the tumor’s outer regions.

Controlling when this oxygen-tolerance feature activates was critical. If it switched on too early, the bacteria could survive in oxygen-rich parts of the body, such as the bloodstream. That would raise serious safety concerns.

What if bacteria could help fight cancer?
Researchers are developing cancer-eating bacteria that grow inside tumors and activate only when it’s safe to do so.#cancer #cancerresearch #clinicaltrials pic.twitter.com/sVP9Xjailu

— Tom Marvolo Riddle (@tom_riddle2025) February 25, 2026

To prevent that risk, the team relied on a natural bacterial communication process known as quorum sensing. Bacteria use chemical signals to measure how many of their own kind are nearby. As bacterial numbers increase, the signal becomes stronger.

Only after enough bacteria have accumulated inside a tumor does the signal reach a level that activates the oxygen-resistant gene. Researchers say this timing ensures the bacteria gain extra survival ability only when they are securely established inside the cancer.

Fluorescent tests confirm timing control

In an earlier study, scientists showed that Clostridium sporogenes could be genetically altered to better withstand oxygen. In a follow-up experiment, the team tested the quorum-sensing system by programming the bacteria to produce a green fluorescent protein.

The bacteria began to glow only after reaching a specific population size. This visual signal confirmed that the system activated at the intended moment and remained inactive when bacterial numbers were low, an important safety feature.

Dr. Brian Ingalls, a professor of applied mathematics at Waterloo, compared the design to an engineered circuit. Using tools from synthetic biology, researchers assembled DNA components that each perform a specific role. When combined, they form a system that behaves in a controlled and predictable way.

Research moves toward pre-clinical testing

The next phase of the research will combine both the oxygen-tolerance gene and the quorum-sensing system into a single bacterium. Scientists plan to evaluate the engineered microbe against tumors in pre-clinical trials.

The project began as doctoral research led by Bahram Zargar under the supervision of Ingalls and Pu Chen, a retired professor of chemical engineering. Researchers say the work reflects the university’s emphasis on interdisciplinary health innovation.

The team is now collaborating with the Center for Research on Environmental Microbiology (CREM Co Labs), a Toronto-based company co-founded by Zargar. The partnership also includes Sara Sadr, a former Waterloo doctoral student who played a key role in advancing the research.

Researchers say the collaboration aims to move the experimental therapy closer to real-world testing, with a focus on safety, precision, and long-term medical impact.